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Condensed Matter Physics

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Condensed Matter Physics is the branch of physics that studies the properties and behavior of matter in its condensed phases, primarily solids and liquids. It focuses on understanding the collective phenomena arising from the interactions between atoms and molecules, including crystallography, magnetism, superconductivity, and electronic properties.
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Lucretius I: An Ontology of Motion (Edinburgh University Press, 2018)
by Thomas Nail
The most original and shocking interpretation of Lucretius in the last 40 years. Thomas Nail argues convincingly and systematically that Lucretius was not an atomist, but a thinker of kinetic flux. In doing so, he completely overthrows... more
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Proceedings of the 7th International Conference on Methods and Techniques in Behavioral Research
by Andrew Spink

2010

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A Journey into Quantization in Astrophysics: A collection of scientific papers
by Florentin Smarandache
ABSTRACT
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The Electron is a Charged Photon with the de Broglie Wavelength
by Richard Gauthier
A charged photon and its light-speed helical trajectory form a surprising new solution to the relativistic electron’s energy-momentum equation. This charged photon model is a new model for the electron, and quantitatively resembles the... more
Figure 1. Energy and momentum relationships in the charged photon model of the electron. Since the charged photon’s total momentum circulates along the helix, the value of the transverse momentum Prrans =e can be associated with an _ internally
Figure 2. The de Broglie wavelength generated from the charged photon model of electron. right with velocity v and the charged photon travels along its helical path with velocity c. velocity v,,.,=c /v as the electron travels to the phase 16. Conclusions The de Broglie equation for the electron forms the basis of quantum mechanics, described by the Schrédinger equation for the electron in non-relativistic quantum mechanics and by the Dirac equation in relativistic quantum mechanics. The charged-photon approach may lead to a somewhat more fundamental and unified description of the quantum world than is provided by the current standard model of physics and
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MANAGING AND EVALUATING THE IMPACTS OF LARGE RESEARCH PROGRAMMES
by Trevor Wren BSc MA MPhil PhD MBA

2009

This research was funded by, and implemented within, a UK national research organisation, while the author was the KE and Impact Evaluation Manager responsible for assessing impact on a £15m UK government-funded research programme. This... more
earlier and later stages, linking idea generation to the marketplace:
TABLE 3.1: Grounding methodology and methods in literature best practice
Table 3.2: Three proposed methods within the methodology
TABLE 3.3: Analysis summary for each proposed method
2D analysis matrix with possible assessment ‘grades’ is exemplified in the table below.
TABLE 8.1: Complimentary aspects of the different methods
TABLE 10.1: Method improvements suggested after trial
data matrix analysis, gives the table below gives some case examples. information needed, and enable easier communication of the programme as a whole.
impact research and assessment may differ by impact mechanism (to be developed).
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Quantum-Vortex Electron Formed From Superluminal Double-Helix Photon in Electron-Positron Pair Production
by Richard Gauthier
A superluminal quantum-vortex model of the electron and the positron is produced from a superluminal double-helix model of the photon during electron-positron pair production. The two oppositely-charged (with Q = ±e sqrt (2/α) = 16.6e)... more
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Lukyanchuk et al _ Fano Resonances in Palsmonics
by Hai-Yao DENG
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Surface Oxidation and Reduction of CuO and Cu2O Studied Using XPS and XAES
by Michael Bowker

1996, Surface and Interface Analysis

Abstract Using XPS and x-ray-excited Auger electron spectroscopy (XAES), we have studied the variation in surface composition of CuO and Cu 2 O with a variety of high-vacuum treatments, including vacuum annealing, oxidation and hydrogen... more
Figure 7. The Cu 2p spectra of annealed Cu,0: (i) exposed to O, (3 * 108 L) at 300 K; (ii) then exposed to 1 x 10* LH, at 300 Ww
hydroxide, as shown in Fig. i(a). In addition the Cu 2p XPS peak in Fig. 1(b) showed only a low-intensity satel- lite structure. Vacuum annealing of the sample up to 870 K led to a gradual loss of the O 1s hydroxide
Figure 2. Vacuum annealing of heavily annealed CuO oxidized in 1 x 10-* mbar O, at 773 K for 15 min. Samples annealed for 5 min at temperature indicated. (a) Cu 2p XPS. (b) Cu LMM XAES, showing only the two extreme cases of the annealing procedure represented in (a), i.e. immediately after oxidation and with annealing to 773 K (top two spectra). Also shown (bottom two spectra) are spectra for Cu,0 vacuum annealed to 800 K and Cu metal. (c) O 1s XPS. Vacuum reduced. Extensive vacuum annealing of CuO (~8 h at 800 K) led to a Cu 2p XPS spectrum generally associated with a Cu,O surface with no satellite struc- ture to the main peaks. Thus a sufficiently thick layer of Cu,O could be generated at the surface so that reoxida- tion by oxygen diffusion from the bulk was not signifi- cant. The reduction of the CuO surface on vacuum annealing is, at least to some extent, reversible. The CuO surface could be returned to the fully oxidized state, with a high-intensity satellite structure in the Cu 2p spectra, by heating at 773 K in 1 x 10°* mbar oxygen for 15 min. The surface can therefore be cycled between the fully oxidized state (characterized by a highly intense Cu 2p XPS peak satellite structure) and the reduced state (where this is absent) by heating in oxygen and vacuum annealing, respectively. The tran- sition between these two states is clearly illustrated in Fig. 2(a), which shows the development of the Cu 2p
Figure 4. Changes in the XPS and XAES spectra of a fresh Cu,0 sample on initial vacuum annealing: (a) O 1s; (b) Cu LMM XAES. XPS spectra with vacuum annealing (5 min at a base pressure of ~2 x 10-9 mbar at the maximum tem- perature indicated) following oxidation. The bottom spectrum is characteristic of fully oxidized CuO with a
Figure 3. The O 1s /Cu 2p XPS peak area ratio as a function of annealing temperature for heavily annealed CuO oxidized in 1 x 10~* mbar O, at 773 K for 15 min (from spectra shown in Fig. 2).
Figure 5. Vacuum-annealed Cu,0 exposed to oxygen at 300 K: (a) Cu 2p XPS; (b) Cu LMM XAES; (c) O 1s.
Figure 6. Vacuum annealing of CuO oxidized in 1 x 1074 mbar O, at 773 K for 10 min. Samples annealed for 3 min at temperature indicated: (a) Cu LMM XAES; (b) Cu 2p XPS.
showed no sign of the CuO-related satellite structure. Annealing also led to the formation of Cu metal at the surface. This is clearly distinguished in the Cu LMM x-ray-excited Auger transition by the formation of a
Figure 9. Heavily annealed CuO reduced in 5 x 10-5 mbar H, at 420 K for 10 min and subsequent vacuum annealing: (a) Cu LMM XAES; (b) Cu 2p XPS.
Figure 10. The Cu LMM XAES spectra of Cu,0 reduced in 5 x 10-5 mbar H, at 420 K for 10 min and subsequently vacuum annealed. shown in Fig. 8(a) (i). Hydrogen treatment of the fully oxidized CuO at 400 K in 1 x 10°* Torr H, resulted in more extensive reduction with a further reduction in the Cu 2p satellite intensity [Fig. 8(a) (iii)]. Evidence for Cu metal can be seen from the lower binding energy shoul- der at 568.3 eV on the Cu LMM peak in Fig. 8(b) (iii). The fully oxidized CuO surface could be regenerated by vacuum annealing to 773 K for several minutes.
Figure 11. Schematic representation of the changes in surface composition of CuO (a) and Cu,O (b), with a variety of oxidation and reduction treatments employed in this work. The second type of surface obtained after prolonged vacuum annealing was characteristic of Cu,O. Several authors have reported on the reduction of CuO to form a surface layer of Cu,O during vacuum annealing moni- tored with XPS. Jernigan and Somorjai® report that UHV annealing of CuO at 773 K led to the formation of Cu,O only, with no report of reoxidation to CuO. The reduction of CuO to Cu,O with annealing would be expected from the behaviour of bulk CuO, which decomposes to Cu,O above 1073 K.?3 It is, however, suggested from this previous work that reduction of the surface region begins at considerably lower tem- Two types of surface composition were generated from CuO samples. The first was a fully oxidized CuO surface not subjected to prolonged vacuum annealing and characterized by high-intensity Cu 2p satellites. The second produced after prolonged vacuum annealing contained a thick surface layer of Cu,O and was char- acterized by the absence of an intense Cu 2p satellite structure. The first of these, the fully oxidized surface,
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Nobel Prize on Hoax . Rally Against Nobel Prize 2017 ( physics and Physiology on Fiction and Illusion ) -- Paper Published on 28.10.2017 - 25 days after prize declared
by vijaymohan das
Time is consciousness ( Time mindness or Atomic genes , TM ) present in CCP ( thought script of Anti mind particles ) While Space is Void which is Nothing . How could space create ripples ? A Fake Mathematical Theory of Space Time... more
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Thin-film silicon solar cell technology
by Nicolas Wyrsch and 
1 more
Milan Vanecek

2004, Progress in Photovoltaics: Research and Applications

Amorphous silicon (a-Si:H) layers were first deposited by R. Chittick.’ He was experimenting with silane (SiH4) plasmas and accidentally obtained a-Si:H layers in a remote part of his plasma reactor. Chittick’s results were taken up by W. E. Spear and co-workers at Dundee University, who published* the first systematic study on plasma-enhanced chemical vapour deposition (PECVD) with silane plus (optional) doping gases: Figure | shows schematically the results obtained by W. E. Spear et al.* by plotting the values of dark conductivity and dark conductivity activation energy E,, against gas phase doping ratio. Also plotted is the estimated position of the resulting Fermi level E;, obtained by taking the E, values and correcting for the so-called statistical shift.4 Figure 1. Measured value of dark conductivity o, measured value of activation energy E,, of dark conductivity and estimated position of Fermi level E; for a-Si:H layers, produced by PECVD on glass, in function of gas phase doping ratio Npy3/Nsina (for n-type layers) and Ngou6/Nsina (for p-type layers). Values of o and E, are from,* E,* is here the estimated ‘true’ distance between band edge (E., E,) and the Fermi level E;, where the statistical shift E, has additionally been taken into consideration for n-type layers according to,* assuming thereby a constant defect density of 10'°/cm? eV. For p-type layers, an identical correction E, has been assumed. The equivalent bandgap of a-Si:H, or the ‘mobility gap’ as it is called here, is taken to be 1-7eV, while drawing the graph; this corresponds to the generally published values
Figure 2. Schematical sketch of a typical p—i—n thin-film silicon solar cell, as used both for a-Si:H and for j1c-Si:H. The values for n indicated here give approximate values of the optical index of refraction, an important parameter for light trapping considerations. A glass substrate is assumed here; this corresponds to the so-called superstrate configuration (see Section 4.1)
Figure 3. Measured values of dark conductivity o and of activation energy E,.; of dark conductivity for juc-Si:H layers, produced by PECVD, on glass: as a function of boron content in the deposited layers, as measured by Secondary Ion Mass Spectroscopy (SIMS).!° Boron-free layers are here n-type, because of unintentional doping by oxygen, as shown later. The compensation point is obtained at a doping phase ratio [B2H6]/[SiH,] of about 1 ppm, corresponding to a boron concentration (SIMS) of about 3 x 10!° at/em?. No correction for the statistical shift has been effected here (in contrast with Ficure 1), as the defect densities near the bandedges are assumed to be negligibly small for uc-Si:H layers
Figure 4. Curves for the optical absorption coefficient a and the penetration depth d, = 1/a of monochromatic light with photon energy hy and wavelength 4, for wafer-type crystalline silicon (c-Si) and typical device-quality a-Si:H and juc-Si:H layers on glass.'>:!© The curve for jc-Si:H has been corrected for light scattering due to surface roughness!®
Table I. Values of y°r° products, computed from photo ANd Lamp-Measurements, of amorphous and microcrystalline silicon layers (thickness 1—2 um) deposited on glass substrates Figure 5. Schematic representation of the deformation of the internal electric field E(x), within the i-layer of a p—i—n thin- film silicon solar cell: due to positively charged defects (mainly dangling bonds) D* near the p/i-interface and due to negatively charged defects, (mainly dangling bonds) D™ near the i/n-interface.
For pc-Si:H solar cells, as produced today with reasonable efficiencies, the typical microstructure is as shown in Figure 6. Figure 6. Schematic representation of the microstructure within an jic-Si:H solar cell having a p—i—n structure: one remarks thereby a mixed amorphous-microcrystalline (heterophase) layer, cracks and crystallites embedded in cone-like conglomerates (see also’’). For uc-Si:H layers and cells deposited with a very low concentration of SiH, in H2 source gas, i.e., very far from the a-Si:H/c-Si:H transition, the cracks can be very pronounced and reach right up through the i-layer
Figure 7. Reflectances from cells with TCO of low and high haze, respectively. Measurement is performed with light incident from the glass side, in the glass/TCO/p—i-n/metal configuration
Figure 8. Quantum efficiencies of two identically deposited p—i-n cells on smooth and etch-textured ZnO yoth index grading and light trapping. And the n-layer/back contact interface evidently also plays an important ‘ole. (Thereby, in the superstrate configuration, the roughness of the front layer is largely replicated at the back ontact.)
Figure 9. Quantum efficiency (QE) characteristics of an amorphous silicon p—i—n single-junction cell (see also Table II), deposited on LP-CVD ZnO after light-soaking (800 h at 50°C and under | sun intensity). Owing to the i-layer thickness of only 0-25 um, the cell stabilizes at an NREL confirmed efficiency of 9-47%°°
Figure 10. (a) -V curve of the best microcrystalline silicon p-i-n cell so far fabricated at IMT Neuchatel®! with an AM1-5 efficiency of 8-5%; (b) typical QE characteristics of a jic-Si:H p—i-—n single-junction cell deposited on LP-CVD ZnO (Note that the two curves are measured on two devices with different i-layer thickness)
‘igure 11. Schematic structure of the micromorph tandem cell in the superstrate configuration, i.e., glass/TCO/p—i-n a-Si:H/p-i-n juc-Si:H
Figure 12. Spectral response of a tandem micromorph p-i-—n solar cell, compared with that of a tandem p—i-n a-Si:H solar cell
Figure 13. /(V) curve of a micromorph tandem cell, as fabricated recently by IMT Neuchatel” is given in the initial and light-soaked state (after 336h under 100 mW/cm” and 50°C)
Figure 14. Long-term performance of a BIPV facade at the Bavarian Ministry for Environmental Protection®
Figure 15. Photovoltaic roof integration at the Institute of Microtechnology, University of Neuchatel (courtesy H. Keppnet IMT)
Figure 16. Roof integration with semitransparent a-Si/a-Si modules (3300 m”) on an annex building (Paul-Lobe-Haus) of the German Parliament in Berlin
Figure 17. Facade with semitransparent a-Si/a-Si modules
Figure 18. Facade at the Bavarian Ministry for Environmental Protection (see Figure 14)
Figure 19. Photovoltaic roof on the house of the La Galére Sailing Club in Auvernier near Neuchatel (60 m*, 2400kW h average energy yield per year)
Table II. Typical values of /(V) characteristics obtained for state-of-the-art thin-film silicon single-junction p—i—n solar cells at IMT Neuchatel compared with basic, ‘semi-empirical’ limit values based solely on the bandgap of the material *In the degraded state, i.e., after 800h light-induced degradation at a light intensity of 100mW/cm* AM1-5 close conditions and a temperature of 50°C. The stabilized efficiency value of 9-47%, for the a-Si:H cell has been confirmed by NREL. **These values refer to the best p—i—n-cell fabricated at IMT Neuchatel. Record values for individual parameters are often substantially higher. Thus, Kaneka (Yamamoto et al.°*) report a n-i-p wc-Si:H solar cell with a current of 25-8 mA/cm? and Canon reports a n-i-p jic-Si:H solar cell with a current of 29-96 mA/cm”, FF of 0-7 and V,, of 0-518 V.% A short-circuit current above 30 mA/cm* has been reported by the same group. The Jiilich group (Klein et al.°°) report a p-i-n cell with Vo. of 565 mV and with J,, above 20 mA/cm?.
Table II. Micromorph tandem cell with an intermediate ZnO layer in the initial state and after 1300h light-soaking
Table IV. Typical efficiency reduction factors: from record research cell to production module
Table VI. Annual energy yields, relative performances, and total-area efficiencies (STC and ‘effective’) for various module types, exposed on Mallorca and in the UK (effective efficiency values are corrected for inverter losses) *Now RWE SCHOTT Solar; **data sheet values.
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Solar cell efficiency tables (version 36)
by Keith Emery

2010, Progress in Photovoltaics: Research and Applications

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since... more
Figure 1. (a) Normalized external quantum efficiency (EQE) of three of the new non-concentrator cell entries in this issue plus the Solarmer ‘notable exception’ cell from the previous version [3]; (b) Normalized EQE of four of the new non-concentrator cell entries in this issue plus the 25% efficient Si cell from Table |; (c) Normalized EQE of two of the new concentrator cell entries together of that of the record 41.6% device reported in the previous version [3].
* CIGS = CulnGaSe;; a-Si = amorphous silicon/hydrogen alloy. » Effic. = efficiency. “(ap) = aperture area; (t) = total area; (da) = designated illumination area. “FF = fill factor. °FhG-ISE = Fraunhofer Institut fiir Solare Energiesysteme; JQA = Japan Quality Assurance; AIST = Japanese National - Advanced Industrial Science and Technology. ‘Recalibrated from original measurement. ® Reported on a ‘per cell’ basis. * Not measured at an external laboratory. ‘Light soaked at Oerliken prior to testing at NREL (1000h, 1 sun, 50°C). )Measured under IEC 60904-3 Ed. 1: 1989 reference spectrum. ‘Stability not investigated. References [28] and [29] review the stability of similar devices. ‘Stabilized by 174h, 1 sun illumination after 20h, 5 sun illumination at a sample temperature of 50°C. Table I. Confirmed terrestrial cell and submodule efficiencies measured under the global AM1.5 spectrum (1000 W/m?) at 25°C (IEC 60904-3: 2008, ASTM G-173-03 global).
* CIGSS = CulnGaSSe; a-Si = amorphous silicon/hydrogen alloy; a-SiGe = amorphous silicon/germanium/hydrogen allo » Effic. = efficiency. ° (ap) =aperture area; (da) = designated illumination area. “BF = fill factor. “Recalibrated from original measurement. ‘Light soaked at NREL for 1000h at 50°C, nominally 1-sun illumination. ® Measured under IEC 60904-3 Ed. 1: 1989 reference spectrum. Table Il. Confirmed terrestrial module efficiencies measured under the global AM1.5 spectrum (1000 W/m?) at a cell temperature of 25°C (IEC 60904-3: 2008, ASTM G-173-03 global).
* CIGS = CulnGaSep. » Effic. = efficiency. “(ap)= aperture area; (t) = total area; (da) = designated illumination area. “Recalibrated from original measurement. ®Light soaked under 100 mW/cm? white light at 50°C for 1000h. ‘Stability not investigated. References [28] and [29] review the stability of similar devices. 5 Light soaked under simulated AM1.5 for about 140h prior to shipment to NREL. Table Ill. ‘Notable Exceptions’: ‘Top ten’ confirmed cell and module results, not class records measured under the global AM1.5 spectrum (1000 W/m?) at 25°C (IEC 60904-3: 2008, ASTM G-173-03 global).
Table IV. Terrestrial concentrator cell and module efficiencies measured under the ASTM G-173-03 direct beam AM1.5 spectrum ata cell temperature of 25°C. * Effic. = efficiency. ® (da) = designated illumination area; (ap) = aperture area. ©One sun corresponds to direct irradiance of 1000 W/m’. “Not measured at an external laboratory. “Measured under a low aerosol optical depth spectrum similar to ASTM G-173-03 direct [4 ‘Measured under old ASTM E891-87 reference spectrum. 8 Recalibrated from original measurement.
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Radiation damage in the TEM and SEM
by Marek Malac

2004, Micron

We review the various ways in which an electron beam can adversely affect an organic or inorganic sample during examination in an electron microscope. The effects considered are: heating, electrostatic charging, ionization damage... more
Fig. 1. Classification of radiation damage according to the type of electron scattering and according to the effects produced in a specimen.
Fig. 2. 2 wm X 2pm bright-field TEM image showing defect clusters produced in a thin graphite crystal irradiated at 600°C by 200 keV electrons. If E exceeds some displacement energy Eq which is a property of the specimen material (bond strength, crystal lattice and atomic weight of the constituent atoms), high- angle elastic scattering can displace atomic nuclei to interstitial positions and thereby degrade the crystalline perfection. This effect is most easily seen in the TEM if the specimen is raised to an elevated temperature, such that the interstitials aggregate to form loops or defect clusters which give a characteristic ‘black-white’ diffraction contrast (Fig. 2). Similar effects are seen in metals that have
Fig. 3. Threshold incident energy for onset of electron sputtering in solid elements, calculated using Eq. (2) taking E, as the sublimation energy per atom. in which (J/e) represents the incident-current density in electrons/cm”/s and the remainder of the expression is a sputtering cross-section, here evaluated using a non- relativistic Rutherford-scattering model; E, is in eV and Exnax 18 related to the incident energy through Eq. (2). The case of elemental carbon, shown in Fig. 4, illustrates the fact that the sputtering rate increases rapidly above the incident-energy threshold, comes close to its maximum value at about twice the threshold value and varies relatively little at higher incident energy. Because the sputtering rate is low immediately above the incident- energy threshold, the situation for medium-Z elements is somewhat less serious than might be deduced by immediate inspection of Fig. 3.
Fig. 4. Sputtering rate (in nm/s) at the exit surface of a carbon film versus incident-electron energy Eo, based on relativistic Mott and Rutherford and Mott cross-sections, and as given by Eq. (3).
Fig. 5. Temperature rise (AT) in a carbon film for a 5 nA electron probe, calculated as a function of the probe diameter (d) using Eq. (4) with Ro = 30 pm and k = 1.6 W/m/K. Incident energy = 200 kev.
Fig. 6. Total electron yield (6+ 7) and surface potential (V,) in a poorly conducting bulk specimen or thin film (dashed curve), as a function of incident-beam energy Ep. At low Eo, the beam penetrates only a few nm (or less) and most of the secondaries produced can escape. The larger value of 5(V,) requires V, to be positive in order to achieve current balance. After the beam hits the specimen, the rise in V, causes V,/R, to increase and d(V,) to decrease until Eq. (6) is satisfied. For highly insulating materials (large R,), the
Fig. 7. (a) Array of contamination dots written on a silicon nitride membrane by an electron probe in a 200 kV TEM. (b) 7 nm-wide bismuth line with low line-edge roughness (LER < | nm), produced by contami- nation lithography. utilized as a form of lithography, as proposed long ago by Broers (1964). Because the hydrocarbon polymer has reasonable resistance to etching by chemical solutions or sputtering ions, a dot-array contamination pattern can be used to fabricate an array of magnetic dots with data storage applications; see Fig. 7a. Alternatively, the contamination line formed by a linear electron-beam scan can be used to produce a nano-wire with interesting electrical properties, as in Fig. 7b. In this case, the line- edge roughness (LER) is of importance and the measured values (LER < 1 nm, 30-value) compare favourably with those achievable by e-beam lithography with ultra-thin polymer resists.
Displacement energy E,; and the corresponding threshold value of incident energy Eo, for some common materials (Hobbs, 1987)
: Critical dose D,; for destruction of the electron-diffraction pattern of selected aliphatic and aromatic materials (Reimer, 1975)
Characteristic dose for the removal of specified elements from organic specimens irradiated with 80 keV electrons, determined by EELS (Egerton et al., 1987)
Effect of surface coating on radiation sensitivity of TEM specimens; Pc denotes phthalocyanine. Specimen thickness was in the range 7—50 nm, coating thickness in the range 5—15 nm Data from Salih and Cosslett (1974); Fryer and Holland (1983, 1984); Egerton et al. (1987).
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Solid oxide fuel cell technology—features and applications
by nguyen minh

2004, Solid State Ionics

Solid oxide fuel cell (SOFC) technology has been under development for a broad range of power generation applications. The attractiveness of this technology is its efficient and clean production of electricity from a variety of fuels. The... more
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Green Synthesis of CuO Nanoparticles with Leaf Extract of Calotropis gigantea and its Dye-Sensitized Solar Cells Applications
by Gurdip Singh

2015, Journal of Alloys and Compounds

Green synthesized copper oxide (CuO) nanoparticles (NPs) were employed as electrocatalytic materials for the fabrication of counter electrode in dye sensitized solar cells (DSSCs). Uniform CuO NPs were synthesized by the leaves extract of... more
Fig. 2. XRD patterns of synthesized CuO NPs from leaf of Calotropis gigantea. Fig. 1. Photograph of Calotropis gigantea plant (a), FESEM images (b, c) and EDX spectrum (d) of biosynthesized CuO NPs from leaves extract of Calotropis gigantea.
where K is a constant, « is the absorption coefficient, Epnoton the dis- crete photo-energy, and E, the band gap energy. From this equation, the E, of biosynthesized CuO NPs is calculated to be ~1.86 eV, which is quite high as compared to bulk CuO and similar to reported CuO nanomaterials [32]. This increment in E, value is resulted from the formation of nanostructures in biosynthesis.
Fig. 3. TEM (a) and HRTEM (b) images of synthesized CuO NPs from leaf of Calotropis gigantea. The photovoltaic parameters of fabricated DSSC has been eval- uated by analyzing the current density (J)-voltage (V) curve under the light illumination of 100 mW/cm? (1.5 AM). Fig. 5 shows the J-V curve of fabricated DSSC with the CuO NPs based counter
Fig. 5. J-V curve of DSSC fabricated with counter electrode based on synthesized CuO NPs from leaf of Calotropis gigantea. The reactions (1) and (2) are represented the reduction peak of I3/I- and oxidation peak of Ip/Iz3 in the CV plot [36]. In this case, a reasonably good cathodic current of 0.98 mA/cm? at ~—0.40V is obtained in the electrochemical system based on the synthesized CuO NPs counter electrode, indicating the high electrocatalytic activity toward the reduction of Iz to I” ions in the redox electro-
Fig. 4. FTIR spectrum of synthesized CuO NPs from leaf of Calotropis gigantea.
Fig. 6. Cyclovoltametry plot of counter electrode based on synthesized CuO NPs from leaf of Calotropis gigantea in 10mM Lil, 1mM Ip and 0.1M LiClO, in acetonitrile solution.
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Photoluminesence and FTIR study of ZnO nanoparticles: the impurity and defect perspective
by Umapada Pal

2006, physica status solidi (c)

Published online zzz PACS 78.55.Et, 78.67.Bf, 78.30.Fs
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Bose–Einstein condensation of microcavity polaritons—myth or reality?
by Benoit Deveaud

2006, NANOSTRUCTURES: PHYSICS AND TECHNOLOGY

Abstract. We show that Friedel oscillations of the electron density exist in junctions between quasi-one-dimensional and two-dimensional systems. The backscattering of electrons by the Friedel oscillations can qualitatively explain a... more
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Synthesis and characterisation of materials based on inorganic polymers of alumina and silica: sodium polysialate polymers
by Kenneth Mackenzie

2000, International Journal of Inorganic Materials

Inorganic polymers based on alumina and silica polysialate units were synthesised from dehydroxylated aluminosilicate clay (metakaolinite) condensed with sodium silicate in a highly alkaline environment. Reaction of the aluminosilicate... more
Fig. 1. (A) Viscosity of Na-PSS1 as a function of elapsed time after mixing. (B) Log-log plot of the above data.
Fig. 2. Liquid-state "°Si NMR spectra of: (A) sodium silicate; (B) sodium silicate+ NaOH; (C) polymer composition Na-PSS1 immediately after mixing.
Fig. 3. Liquid-state “°Si NMR spectra of polymer mixtures recorded at the indicated elapsed times (minutes) after mixing: (A) Na-PSS1; (B) Na-PSS (C) Na-PSS7. In an attempt to determine the critical differences between good and poorly curing compositions, liquid-state MR was carried out on mixtures Na-PSS1, Na-PSS2 (with the same oxide molecular ratio as Na-PSS1 but higher water content and did not set) and Na-PSS7 (higher a content and poorer mechanical properties). The *°Si MR liquid spectrum of the initial sodium silicate [Fig. 2(A)] shows the sharp peaks of the Q°, Q', Q? and Q? sites at about —72, —80, —87 and —96 ppm, respectively [17], The Krebs- Stormer viscometer used here is of the shear type in which the rotational motion is applied using a paddle wheel rather than concentric cylinders. Although it is normally used for commercial process control, providing viscosity values expressed in arbitrary units, it may be calibrated with solutions of known viscosity [14]. Since its
Fig. 4. FTIR spectra of metakaolinite and selected polymer compositions after curing and drying. Fig. 3(A) shows that in the mixture Na-PSS1 the intensity of the broadened but diagnostic sodium silicate resonances progressively decreases over the first 7 h of the reaction, as the silicate is consumed by the formation of the polymer. The *°Si spectrum remaining after the disappearance of the sodium silicate peaks consists of the original broad signal from the glass tube, with an extended downfield shoulder originating from the solidified polymer. By contrast, the sequence of spectra of mixtures Na- PSS2 and Na- PSS7 [Figs. 3(B) and (C)] shows that although the silicate resonances are broadened by the addition of metakaolinite, suggesting some initial interaction, their intensities remain virtually unchanged up to 15 h after
Fig. 5. Typical XRD powder diffraction patterns of the starting materials and selected polymer compositions after curing and drying. Asterisks mark the major reflection of quartz (PDF No. 33-1161). The metakaolinite spectrum [Fig. 4(A)] is typical, with broad bands at about 3450 cm‘ and 1650 cm ' from adsorbed atmospheric water, an Si-O stretching vibration at 1088 cm~', an Si-O-Al] vibration at 810 cm~' and an
Fig. 6. 11.7 T solid-state MAS NMR spectra of the starting material and selected polymer compositions after curing and drying: (A)-(D) *’Al spectra; (E)-(H) *°Si spectra; (I)-(L) *°Na spectra. The ’’Al spectrum of the initial metakaolinite [Fig. 6(A)] is typical of this phase, showing broad overlapping resonances at 52 ppm (tetrahedral), 10 ppm (octahedral) and a resonance at 28 ppm which is often attributed to Al in 5-fold coordination with oxygen [21]. When the metaka- olinite is mixed with the other polymer-forming con- stituents, the Al coordination immediately changes to The kaolinite starting material [Fig. 5(A)] shows the
Fig. 7. 11.7 T *7Al MAS NMR spectra of several PSS polymer compositions cured at 65°C, plotted on the same intensity scale. The “’Al spectra shown in Fig. 6 have been scaled to the same vertical height, masking considerable differences in the spectral intensities. As shown in Fig. 7, when plotted on the same intensity scale, all the ’’Al spectra are much weaker than that of the well-polymerised PSS1, having integrated intensities ranging from 3.4 to 11% of PSS1, even for samples of the same Al content as PSS1 (Fig. 7). Since the Al is not physically lost from the solid system, having not been detected by solution NMR, the loss of Al signal from the less-well-polymerised samples is probably due to its occurrence in poorly ordered regions in which the signal is broadened beyond detection. Such a phenom- enon particularly affects quadrupolar nuclei such as *’Al, and has been found to occur when a crystalline aluminosilicate such as kaolinite is amorphized by thermal dehydroxylation [22]. The greatly increased *’A1 intensity of sample PSS1 is a reflection of its more ordered polymerised structure.
Fig. 8. (A) Proposed semi-schematic structure for Na-polysialate polymer. (B) Three-dimensional framework structure based on a suggested model for K-polysialate polymer, after Davidovits [2]. ®, SiQ,(3A1) site; *, SiQ,(2A1) site; 6, SiQ,(1A]) site; @, AlQ,(4Si) site.
“Ignition loss at 950°C. Chemical composition of the starting materials
Polymer compositions of this study
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THz imaging and sensing for security applications---explosives, weapons and drugs
by Filipe Oliveira

2005, Semiconductor Science and Technology

Over the past 5 years, there has been a significant interest in employing terahertz (THz) technology, spectroscopy and imaging for security applications. There are three prime motivations for this interest: (a) THz radiation can detect... more
Figure 1. (a) THz absorption spectra from [13]. (b) Comparison study of transmission spectra of RDX using THz-TDS and FTIR (Fourier transform infrared) spectroscopy with data from [13, 14]. The dashed line is RDX from [13]. The other curves are from [14] where the bottom curve is RDX measured by THz-TDS, the solid curve is RDX measured by FTIR, and the top curve is C4 measured by THz-TDS). The sharp features in C4 (THz-TDS) are remnants of water. Note that the absorption features at 0.8, 1.5, 2.0, 2.2 and 3 THz are exhibited in both the datasets. The spectral feature at 1.1 THz is not present in both datasets.
Figure 2. (a) THz spectra of ammonium nitrate (1 mm thick sample). The dotted line corresponds to measured data of [22]. The dashec line is from [16]. (b) Extended transmission spectra [22] out to 21 THz with nominal sample thickness listed.
Figure 3. Atmospheric transmission bands in the terahertz range of frequencies (after [8]).
Figure 4. Illustration of a potential implementation of a THz imaging array in transmission mode (a) and reflection mode (b).
Figure 5. Schematic of THz detection of explosive hidden behind a barrier material using a dual pass transmission geometry.
Figure 7. Calculation of detected THz power through a corrugated cardboard (1.4 dB mm~!) of 0, 3, 6 and 9 mm thickness. The attenuation coefficients of the barrier materials, atmosphere and air are taken from experimental measurements. Note that the 0.1 mm thick RDX level is easily detectable up to distances of 25 m even with multiple layers of the barrier material. Figure 6. Calculation of detected THz power through a Ski jacket (1.9 dB m7) of varying thickness 0, 3, 6 and 9 mm (curves top to bottom). Zero thickness corresponds to no jacket. The attenuation coefficients of the barrier materials, atmosphere and air are taken from experimental measurements. The horizontal line corresponds to the estimated Pin of the system. The thickness of the explosive 0.1 mm. Note that the detected power is sufficiently large to detect the thin layer of explosive even at a distance of 25 m.
Figure 8. Calculation of detected THz power through a wool sweater (5.4 dB mm7') of thickness 0, 3, 6 and 9 mm fora transmission geometry. The attenuation coefficients of the barrier materials, atmosphere and air are taken from experimental measurements. Note that since the wool sweater is so much more scattering (high attenuation coefficient) compared to other materials, the effective range is greatly reduced for multiple layers. An explosive hidden behind a 3 mm thick sweater can be detected up to 25 m. A 6 mm sweater restricts the effective range to <8 m.
Figure 9. A THz emitting object in the shape of the NJIT logo. The number of detectors in the circular imaging array is N = 49, N= 100 and N = 200 from left to right. The distance to the object is 25 m with a ~35° field of view. The images are unprocessed (uncleaned). After processing to remove imaging artefacts, the image quality can be dramatically improved.
Figure 10. Theoretical calculation of a THz image generated by an interferometric imaging array. The NJIT logo, 0.8 m x 0.3 m/, is imaged using a circular array of 100 equally spaced detectors with a radius of 0.1 m. The imaging array is optimized for a 25 m distance. Note that the image decreases in size as the target recedes from the imaging array. The bottom two images have been cleaned using the point spread function of the imaging array.
Figure 11. Bitmap of MLP and RBF analyses of bomber problem (print version: white = metal, black = RDX, light grey = background/ unknown, medium grey = skin/candy) (online version: white = metal, red = RDX, orange = candy, green = skin, grey = background and blue = unknown).
* Samples are prepared as pellets using spectrographic-grade polyethylene. > Samples are ordered as compressed pellets from Accurate Energetics LLC. All materials are in sensitized form (water-free). Table 1. Collection of absorbance peak positions of some explosives and drugs. Conversion to units of wavenumbers requires multiplication by 33 cm! = 1 THz.
Table 2. Estimated phase error 5 from imaging a 2.5 cm object at various distances using 1 THz radiation. The baseline 5 is an estimate of the physical size of the imaging array. Note that for distances of 5—10 m, the size of the imaging array is 6-12 cm suggesting that a hand-held unit might be achievable. where the denominator of equation (4) has been approximated as 1/rirz © 1/Z). If an object is in the far-field (8 < 1), the phase shift 6 = k(x? —xp+y?— y3) /2Zo can be neglected and equation (4) will relate the coherence function in the antenna plane to the brightness distribution of the source(s). By a Fourier transform, the brightness distribution (image) can be reconstructed by measuring the coherence function for a given arrangement of detectors in the sensor array. Imaging with a significant phase shift results in poor image quality (extremely blurred).
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Solar Planets Order disproves the Gravity Theory.doc
by Gerges Tawadrous
- The Solar Planets order proves that, the planet orbital distance is defined based on his Diameter and NOT his Mass, which disproves the Gravity Theory.. But - Planet Diameter and Orbital Distance Relationship Equation is so hard to... more
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LENRs enable green radiation-free nuclear power and propulsion
by Lewis Larsen

2019, Lattice White Paper: LENRs enable green radiation-free nuclear power and propulsion

If commercialized, LENRs could become one of the world’s preeminent energy technologies. At system electrical power outputs of just 5 - 10 kwh, modular LENR-based distributed power generation systems providing combined heat and... more
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The Charged-Photon Model of the Electron, the de Broglie Wavelength, and a New Interpretation of Quantum Mechanics
by Richard Gauthier
This article continues to develop the charged-photon model of the electron. In particular, the relativistic de Broglie wavelength of a moving electron is derived from the model. De Broglie’s own derivation is also summarized and compared... more
Figure 1. De Broglie wavelength generated from charged photon model of electron (computer graphic thanks to Chip Akins)
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Proceedings of the 7th International Conference on Design and Emotion
by Jörn Altmann

2010

Several Mediterranean countries are suffering from water scarcity, unsustainable management of water resources, vulnerability to climate change, pollution and lack of sanitation infrastructure and suitable treatment technologies. These... more
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Introduction to MerKaBa Mechanics
by Mohsen Paul Sarfarazi
An overview of the mechanics of MerKaBa with direct reference to the author’s space-time theory/model of nested spherical dimensions of cosmos is presented. It is emphasized that the spherical dimensional edifice of cosmos may be... more
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Paleoluminescence Laboratory
by Yavor Shopov
The laboratory uses methods and equipment developed at the Physics Department. They are subject to three Bulgarian inventions, and one Canadian patent of our laboratory’s team. Some of the devices developed, and used by the laboratory... more
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THE IMPACTS OF NATIONAL SCIENCE AND TECHNOLOGY FUNDING IN THE UK: A PUBLIC MANAGEMENT EVALUATION SUMMARY
by Trevor Wren BSc MA MPhil PhD MBA
This Impact Report identifies and summarises the diverse impacts, resulting from the £500m of UK funding of Science and Technology in 2013, using numerous quantitative metrics and short case study extracts. It shows how the varied... more
Observation of the Higgs boson by the ATLAS experiment at CERN. (Credit: CERN).
Harwell Oxford, one of the UK's foremost Science and Innovation Campuses.
Professor Peter Higgs visits the CMS experiment at CERN. (Credit: CERN).
The structure of graphene. (Credit: Dreamstime) Characterising graphene
Image of the Galileo satellites, part of Europe's new global navigation satellite system. (Credit: ESA). manipulate increasingly large and more complex data set: The power of computing developed to analyse massive and mixed scientific data sets in turn transforms industry and everyday life. STFC and our predecessors have been at the forefront of computing knowhow for the past 50 years. During this time, we have led the way across the whole spectrum of computing capabilities, from high performance computing facilities and digital curation, to graphics and software, from networking to grid infrastructure and the World Wide Web.
Timeline of key space missions, in all of which the UK and STFC have played a significant role.
Daresbury Laboratory Tower. >IrC nas partnered with the lecnnology strategy board as a ‘cluster champion’ to deliver business support as part of its Launchpad competitions. The £2 million Materials and Manufacturing Northwest Launchpad? is designed to accelerate new business projects and stimulate start-up businesses centred around the cluster of materials and manufacturing companies at Sci-Tech Daresbury and the Runcorn Heath Business and Technical Park. A key aim of the scheme is also to strengthen this cluster and STFC, as its chosen cluster champion, will deliver business support services to successful applicants. The Technology Strategy Board are learning from STFC’s business and investment support activities to enhance and improve their future Launchpad competitions and overall SME support programmes.
Visualisation suite at the Hartree Centre, Daresbury Laboratory. The Hartree Centre focuses on partnerships with business and academia to unlock the commercial opportunities offered by high performance computing systems. This has the benefit of utilising and growing UK skills in this area and has attracted IBM as the major partner to develop these opportunities. The Centre is working closely with a number of major companies such as Unilever, where we have established a forma research partnership.
A division of De Beers, Element Six is an international
Astrophysics research supported by STFC led to the concept of a plasma device that generates ozone inside sealed containers. Ozone is a powerful disinfectant and this device provides a new way to make food safer for consumption, and prolongs its shelf-life. The device can be used after packaging and aims to cut down on the 7 million tonnes of food waste that is created every year in the UK®. Follow- on Funding from STFC was granted to develop the device and engage with industrial partners to explore possible applications. A company called Anacail was spun-out of Glasgow University in 2011°’ to commercialise this product. Anacail is initially being targeted at the food packaging industry, worth £9 billion in 2010%, and is set to undergo trials on production lines at several UK food processing plants®. Anacail have also been supported by EPSRC throiioh their Collahorative Trainino Accoriint fiind The Innovations Partnership Scheme is designed to transfer technology and expertise developed through STFC funding to the marketplace in partnership with industry and other academic disciplines. STFC technology or expertise must be integral to the project and can be developed with STFC funding at UK higher education institutes, STFC aboratories, CERN and ESO. In 2012/13, we awarded funding to 11 projects, each with an industrial partner. STFC committed £1.7million, which leveraged a further £800K from the industrial partners. University College London spin-out, Zeeko®, have benefited from the support of this scheme. In collaboration with Glyndwr University, they have been the first collaboration in the world to gain acceptance by ESO for their polished mirrors designed to be deployed in the E-ELT® - a significant achievement for the UK's optical manufacturing industry. Glasgow University in 2011°” to commercialise this product.
Students taking part in the ‘Explore your Universe’ programme, a joint programme between STFC and the UK Association for Science and Discovery Centres. Ernest Rutherford Fellowships STFC Ernest Rutherford Fellowships are prestigious awards awards 12 new fellowships each year and in the 2012/13
We currently host 24 apprentices and our scheme has Laboratory. This year the Science Mi pathway for 250 apprentices by 20 apprenticeships are intended to con been running for 20 years. Each apprenticeship offers 4 years paid training in electronic, electrical and mechanical engineering. 70% of the apprentices that have been taken on are still working at STFC’s Rutherford Appleton nister David Willetts aunched'” the first ever Higher Apprenticeship in Space Engineering! with the aim of providing a national 5. These new tribute to UK space industry by supplying advanced skil drive economic growth. s and knowledge to years paid training in electronic, electrical and mechanical
“The sections focus on areas of importance to demonstrate impact; publications, collaborations, further funding, staff development and next destina- tions, technology development, IP and licensing, spin-outs, measures of esteem, public engagement, and use of facilities.
Our performance compared to the leading scientific nations in this area can be illustrated by the following graph: The graph clearly shows that the UK is the best country in the world in particle physics citation impact and has held this position from 2008 to 2011.
The graph clearly shows that the UK is one of the best countries in the world in nuclear physics citation impact. We have been consistently 2nd in the world and have showed a year-on-year improvement in citation impact for the past 4 years. Our performance compared to the leading scientific nations in this area can be illustrated by the following graph:
This profile shows that between 2003 and 2012, STFC publications performed better than UK physical sciences as a whole. The profile curve for STFC (orange curve) is clearly to the right of that for UK Physical Science research (blue curve), indicating more well-cited papers:
Appendix 3 - Interim evaluation results for Explore your Universe
Astronomy
Particle Physics
Nuclear Physics
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Thermoelectric effects in graphene nanostructures
by Viet Hung Nguyen

2015, Journal of physics. Condensed matter : an Institute of Physics journal

The thermoelectric properties of graphene and graphene nanostructures have recently attracted significant attention from the physics and engineering communities. In fundamental physics, the analysis of Seebeck and Nernst effects is very... more
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Quantum-Vortex Electron Formed From Superluminal Double-Helix Photon in Electron-Positron Pair Production
by Richard Gauthier
A superluminal quantum-vortex model of the electron and the positron is produced from a superluminal double-helix model of the photon during electron-positron pair production. The two oppositely-charged (with Q = ±e sqrt(2/α) = 16.6e)... more
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MOLCAS: a program package for computational chemistry
by Ulf Ryde and 
1 more
Per-Åke Malmqvist

2003, Computational Materials Science

The program system MOLCAS is a package for calculations of electronic and structural properties of molecular systems in gas, liquid, or solid phase. It contains a number of modern quantum chemical methods for studies of the electronic... more
The RASSCF wave function specifications can be summarized as:
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Bose-Einstein condensation in dilute gases - Pethick C.J., Smith H.
by Fauzi Ahmad
The study of Bose–Einstein condensation in dilute gases draws on many different sub fields of physics. Atomic physics provides the basic methods for creating and manipulating these systems, and the physical data required to characterize... more
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Metamaterials-based enhanced energy harvesting: A review
by Zhongsheng Chen

2014, Physica B: Condensed Matter

Advances in low power design open the possibility to harvest ambient energies to power directly the electronics or recharge a secondary battery. The key parameter of an energy harvesting (EH) device is its efficiency, which strongly... more
Fig. 1. Schematic diagram of generalized energy harvesting process. The history of metamaterials started in 1968 when a theoretical investigation was first proposed by Russian physicist Veselago for electromagnetic waves (EMW) | 13]. More recently, the metamater- ial concept has been extended in parallel to elastic and acoustic waves (EAW) based on the similarity between the EMW and the EAW. Experimental results have revealed that metamaterials can exhibit exotic properties not easily achieved using naturally occur- ring materials, such as negative permittivity, negative permeability, and so on. According to currently published literatures, metamater- ials used for energy harvesting mainly include phononic crystals, acoustic metamaterials, and electromagnetic metamaterials. Acoustic metamaterials are currently in the stage of infancy anc most of the works were explored theoretically. Li and Chan [25 theoretically validated the possibility of the existence of acoustic metamaterials and pointed out that negative effective mass density and bulk modulus could be achieved simultaneously. Zhang [26 presented the first experimental demonstration of focusing ultra- sound waves through a flat acoustic metamaterial lens composed of a planar network of sub-wavelength Helmholtz resonators Fang et al. [27] proposed a new class of acoustic metamaterial which consists of a 1-D array of Helmholtz resonators which exhibits dynamic effective negative modulus. The design, development anc characterization of acoustic metamaterials still bring forth many challenges and opportunities in materials science [24].
Fig. 2. Classification of materials based on the permittivity and permeability [28] Pendry et al. [29] firstly presented a thin wire component producing negative permittivity and positive permeability and then proposed a split ring resonator (SRR) producing negative perme- ability and positive permittivity [30]. Their innovative works opened up the new research area of metamaterials. Later Smith et al. [31,32] synthesized successfully the first left-handed substance producing negative effective permittivity and permeability, and verified a negative refractive index by practical experiments. Electromagnetic metamaterials have particular properties, such as negative-refractive Vibroacoustic energy harvesting (VAEH) has received extensive attentions over the past decades. Basic conversion mechanisms include piezoelectric, electromagnetic, electrostatic, and magne- tostrictive transduction. However, traditional VAEH methods are often based on linear dynamics. Under this condition, a VAEH device has to be designed to operate optimally at or very close to resonance, so that its electrical output can reach the maximum value. Otherwise, its electrical output will drop dramatically when it is at non-resonance [35,36]. However, it is fatal that the resonant bandwidth of a traditional linear VAEH device is very small.
Fig. 3. The structure of the phononic crystals-based vibration energy harvester [35].
Fig. 5. Experimental energy harvesting configurations (a) with and (b) without the PAM configuration [50]. Fig. 4. Acoustic energy harvesting based on phononic crystals [46].
Chen et al. [42] explored one-dimension phononic piezoelectric cantilever beams to widen the resonant bandwidth of a harvester
Fig. 8. Acoustic funnel formed by the periodic arrangement of stubs [50]. The second one is to use a 2-D lattice structure with an imperfec- tion, which features a periodic array with an internal defect. The localization of the energy at the imperfection can be exploited for tuned energy harvesting purposes and the fundamental idea is to
Fig. 6. Comparison of piezoelectric energy harvesters (a) with and (b) without the PAM configuration [50] Carrara et al. [50] studied deeply metamaterial-inspired structures and concepts for elastoacoustic wave energy harvesting and exploited metamaterial-based and metamaterial-inspired electroelastic systems for performance enhancement in piezoelectric power generation. The metamaterial energy harvester (MEH) can enhance harvesting structure-borne elastoacoustic waves. In particular, they proposed
Fig. 7. 2-D lattice structure made of aluminum stubs with an imperfection [50].
Fig. 9. The fabricated metamaterial (a) and enhanced WPT system (b) with CMR [75].
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Fluidity of aluminum alloys and composites: A review
by Madhusudan Chakraborty

2008, Journal of Alloys and Compounds

Fig. 1. Effect of impurities on casting fluidity of pure Al cast in sand mold [2]. K.R. Ravi et al. / Journal of Alloys and Compounds xxx (2007) xxx-xxx
K.R. Ravi et al. / Journal of Alloys and Compounds xxx (2007) xxx-xxx Fig. 2. Spiral fluidity of binary (a) Al-Cu [3], (b) Al-Si [3] and (c) Al-Mg [3] alloys cast in permanent mold.
Fig. 3. Effect of trace addition on casting fluidity of pure Al cast in sand molc [15].
Fig. 4. Spiral fluidity of A356 alloy containing 0, 10 and 20 vol.% SiC at different temperatures cast in permanent mold [25]. Cooksey et al. [2] observed that the fluidity versus compo- sition relationship is roughly the inverse of the viscosity versus composition relationship in Al—Si system. Existence of a similar reciprocal relationship between fluidity and viscosity is reported in Fe—Cu-S [28] alloy system. However, in the case of composite slurries, a strict reciprocity is seldom observed between the mea-
K.R. Ravi et al. / Journal of Alloys and Compounds xxx (2007) xxx-xxx Fig. 5. Variation of spiral length for A356-15 vol.% SiC with varying holding time at (a) 750 °C and (b) 800°C [27]. 2.4. Surface tension and oxide film sured fluidity decrease and the measured or computed viscosity increase as a result of particle addition.
Fig. 6. Fluidity vs. vol.% of SiC particles in A356 and A357 cast in permanen mold [54].
Fig. 7. Fluidity vs. particle size of mica in Al-4.5% Cu alloys cast in permanent mold [55]. The morphology of the reinforcement influences the fluid- ity of composite melts because of its effect on the surface area to volume ratio of the dispersed phase. Increasing angularity
Fig. 8. Variation of spiral fluidity (cast in permanent mold) as a function of specific surface area of ceramic particles [50].
Fig. 10. Different mode of solidification of alloys: (a) columnar growth and (b) equiaxed growth [58]. Fluidity is generally inversely proportional to the solidifica- tion range [21,57,58]. High fluidity is commonly found to be associated with pure metals and eutectic alloys, wherein solid- ification takes place by the advance of plane interface from the mold wall with the metal flow continuing until the channel is finally choked (Fig. 10(a)). On the other hand, in alloys, constitu- tional undercooling and other phenomena produce independent crystallization in main liquid mass, leading to the presence of free crystals in the liquid, which can arrest the flow and hence reduce the fluidity (Fig. 10(b)). Further, the hindrance caused by crystals with irregular growth surfaces in long freezing range alloys is much greater than that of comparatively smooth crystal- ization interface front of pure metals and eutectic alloys. Thus, fluidity values of pure metals and eutectic alloys are greater than those of alloys solidifying over a temperature range. This is the reason for the wide practical preference for eutectic or near eutectic alloys for foundry purposes, particularly for cast- ing with thin sections. However, a recent study by Han and Xu
Fig. 9. Fluidity vs. particle shape of SiC in A356 alloys cast in permanent mok [55].
Fig. 11. Effect of metal mold temperature and pouring temperature on casting fluidity of Al and its alloys on cast iron mold [4].
Keywords: Fluidity; Aluminum alloys; Metal matrix composites; Thin wall casting Thin wall casting of aluminum alloys and their composites provide new opportunities for aerospace and automotive industries in producin, light weight structures with good mechanical properties. These opportunities can be realized only when the foundries are confident in their abilit: to produce thinner-wall castings. The primary issue that must be addressed in producing thin wall castings is fluidity. The fluidity of aluminun alloys and composites has a direct influence not only on material castability, but also on the casting properties. Fluidity is a complex parameter tha is affected by the properties of the molten metal and mold, pouring conditions, reinforcement characteristics and solidification mechanism. Thi paper brings out the current understanding about the various factors influencing the fluidity of aluminum alloys and composites. Further, theoretica model available in the literature to predict the fluidity of aluminum alloys and their composites is given and its significance has been discussed. © 2007 Elsevier B.V. All rights reserved. 0925-8388/$ — see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.02.038
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Characterization of PbS Nanoparticles Synthesized by Chemical Bath Deposition
by Diwaker Kumar

2009, Journal of Alloys and …

Fig. 1. XRD pattern of PbS nanoparticles.
Fig. 2. (a) PbS nanoparticles produced by chemical bath deposition method with bath temperature around 26°C. (b) PbS nanoparticles produced by chemical bath deposition method with bath temperature around 4°C.
Fig. 3. Variation of (whv)* with energy for nanocrystalline PbS thin film.
Fig. 4. FTIR pattern of PbS nanoparticles.
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QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials
by A. Kokalj and 
2 more
Christos Gougoussis
Stefano de Gironcoli

2009, Journal of Physics: Condensed Matter

QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and... more
Figure 1. Snapshot of the web interface used for undergraduate teaching at MIT. The software has been developed at the MIT’s Office of Educational Innovation and Technology.
Figure 2. Snapshot of the PWgui application. Left: PWgui’s main window; right: preview of specified input data in text mod
Figure 3. Scalability for medium-size calculations (CP code). CPU time (s) per electronic time step (left panel) and speedup with respect tc 32 processors (right panel) as a function of the number of processors and for different numbers mask of task groups, on an IBM BlueGene/P (BG/P) and on an SGI Altix. The system is a fragment of an Af-peptide in water containing 838 atoms and 2311 electrons in a 22.1 x 22.9 x 19.9 A° cell, ultrasoft pseudopotentials, point, 25 and 250 Ry cutoff for the orbitals and the charge density respectively.
Figure 4. Scalability for large-scale calculations: wall time (left panel) and speedup (right panel) as a function of the number of processors. PSIWAT: PWscf code, Npoot = 4, Mask = 4, on a Cray XT 4. The system is a gold surface covered by thiols in interaction with water, 4 k-points, 10.59 x 20.53 x 32.66 R cell, 587 atoms, 2552 electrons. CNT (1): PWscf code, nia = 4, on a Cray XT 4. The system is a porphyrin-functionalized nanotube, I" point, 1532 atoms, 5232 electrons. CNT (2): CP code on a Cray XT3, same system as for CNT (1), Times for PSIWAT and CNT (1) are for 10 and 2 self-consistency iterations, respectively; times for CNT (2) are for 10 electronic steps plus 1 Car—Parrinello step, divided by 2 so that they fall in the same range as for CNT (1).
Table 1. Summary of parallelization levels in QUANTUM ESPRESSO. tuned to the specific application and to the specific architecture. This remarkable characteristic makes it possible for the main codes of the distribution to run in parallel on most or all parallel machines with very good performance in all cases.
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Bose-Einstein condensation of microcavity polaritons
by R. André

2005, physica status solidi (b)

The strong coupling of light and excitons in a two-dimensional semiconductor microcavity results in a new eigenstate of quasiparticles called polaritons. Microcavity polaritons have generated much interest due to the wealth of interesting... more
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Production and Storage of Energy with One-Dimensional Semiconductor Nanostructures
by Abhijit Ganguly

2014, Critical Reviews in Solid State and Materials Sciences

This article outlines state-of-the-art energy technologies, including production and storage, available to us through semiconductor nanomaterials. The nanostructure growth processes have been illustrated in detail, with emphasis on the... more
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Nanoparticles Ni and NiO: Synthesis, characterization and magnetic properties
by Zeinab Fereshteh

2009, Journal of Alloys and Compounds

The present investigation reports, the novel synthesis of nanoparticles Ni and NiO using thermal decomposition and their physicochemical characterization. The nanoparticles Ni powder have been prepared using... more
Scheme 1. Schematic diagram illustrating the formation of NiO nanoparticles.
Fig. 1. XRD patterns of the (a) Ni and (b) NiO nanoparticles. The XRD pattern of the fresh nickel nanoparticles, shown in Fig. 1a, shows the face-centered cubic (fcc) structure of nickel. The peaks are extremely broad. Three characteristic peaks at 44.58°, 51.9°, and 76.54° for fcc nickel (JCPDS, no. 03-1051) marked by their
Fig. 2. FT-IR spectra of (a) oleylamine (b) Ni nanoparticles and (c) NiO nanoparticles. FT-IR spectroscopy is a useful tool to understand the functional group of any organic molecule (Fig. 2a—c). The presence of oley- lamine group on Ni nanoparticles (Fig. 2b) is indicated by the N-H wagging mode from 650 to 900cm~!; NH2 bending modes at 909, 964 and 993 cm~!; and NH scissor mode at 1568 cm~! [29]. The spectrum shown in Fig. 2b also reveals the characteristic peak of the C-N stretch at 1042 cm~! which suggests that the C-N bonds in amine groups, and therefore oleylamine ligands, remain intact, capping the Ni nanoparticles. The peak at 1468cm~' is associ- ated with the C-H bending mode and the two peaks at 2865 and 2921 cm! represent the C-H stretching modes of the oleylamine carbon chain. The presence of various N-H peaks suggests that amines are bound to the surface of the Ni nanoparticles. Based on the FT-IR data, we deduce the following reaction mechanism. Upon injection of [Ni(aceto)2 | and oleylamine into hot TPP solution, the Ni-O bond is cleaved by the oleylamine group and Ni is subse- quently reduced. The weak peaks at 3435 cm~! has been assigned to the EtOH used in the separation step. The presence of various N-H peaks suggests that amines are bound to the surface of the Ni nanoparticles. There was no evidence of free precursor, nickel 2-
Fig. 3. (a and b) TEM images of sample (the inset shows the ED pattern) and (c) HRTEM image of the sample.
Fig. 5. Magnetization versus applied at 300 K for (a) Ni and (b) NiO nanoparticles. reaction was carried out at 245°C, most organic molecules were decomposed. Since only a few oleylamine molecules were adsorbed on Ni nanoparticles. The ED pattern (Fig. 3b) indicates that the Ni nanoparticles are single-crystalline. This high-resolution TEM
Fig. 4. UV-vis absorption spectrum of the NiO nanoparticles.
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Decoherence in solid-state qubits
by Luca Chirolli

2008, Advances in Physics

Interaction of solid state qubits with environmental degrees of freedom strongly affects the qubit dynamics, and leads to decoherence. In quantum information processing with solid state qubits, decoherence significantly limits the... more
Figure 8. Scanning electron micrograph of the Delft flux qubit (small loop with three Josephson junctions) and attached SQUID (large loop) [92] (With permission from the Authors).
Figure 10. Measured probability of state “1” versus microwave excitation frequency w/27 and bias current J for a fixed microwave power for a phase qubit, obtained from Ref. [112]. Dotted vertical line indicate spurious resonators. (With permission from the Authors).
Figure 9. a) Schematic representation of the phase qubit circuit, constituted by a current-biased Josephson junction. b) Anharmonic potential U(6) showing the two lowest energy states |0) and |1), separated by an energy splitting Ho1. The plasma frequency wy» is given by the local quadratic curvature of the potential at the bottom of the well, and AU is the potential barrier that separates the two energy levels in the well from a continuum of levels on the right side of the barrier.
Figure 1. Scanning electron micrograph of a double quantum dot. [17] (With permission from the Authors).
where 3 = kpT and the m- appears in the Hamiltonian for the system-bath coupling, m being related to the topology of the dissipative circuitry. However, the most efficient source of dissipation for flux qubits is represented by fluctuations in the external circuit that produce fluctuating magnetic fluxes through the loop. The coupling of flux degrees of freedom of the qubit to the dissipative environmental elements is well described in the graph formalism described in [96]. In the Born-Markov approximation, it can be shown that the Redfield tensor, written in the eigenbasis {|n)} of Hg, is entirely determined by In the two-level approximation, the rates for transitions from the two-level subspace to higher states can be neglected, and Eqs. (117) and (119) simplify and the dynamics of the 2 x 2 density matrix of the system can be cast in the form of Bloch equations for the dynamics of a pseudo spin 1/2. In this framework the relaxation matrix contains just two rates, Ty ' and Ty ! for the decay of the longitudinal and transverse pseudo spin component, respectively. The latter in turn is limited by relaxation time J; and pure dephasing time Ty, 1/T2 = 1/27, + 1/Ty, and the two rates are given by [96]
Figure 3. Decay of the driven Rabi oscillation in ESR showing a power law decay x 1/\/t and a universal phase shift of 7/4, as given by Eq. (57), valid for t >> max(1/c, 1/bac, bac/207). For the plot the value b = o = 0.4 Ghz have been chosen.
Figure 4. Three-level system. The states 1(2) are spin-up (-down) conduction-band (Ec) electron, with splitting given by gus Btot + dhz, where dhz is the z component of the nuclear field fluctuations. State 3 is a trion with J,, = 3/2 (With permission from the Authors).
Figure 5. Schematic representation the apparent momentum dependent field Q(p) in the spin-orbit Hamiltonian, Q(p)-o, for the Dresselhaus and Rashba spin-orbit interactions.
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The Earth moves with light velocity relative to the sun
by Gerges Tawadrous
The Earth moves with C velocity (light velocity) relative to the Sun i.e. The light is produced by The Earth Motion, where The Earth transforms her motion mechanical waves into light waves, producing the light beams These light... more
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Time to Redefine Physics
by vijaymohan das
Einstein got ZERO Marks on the assumption of Space Time Gravity Theory calling Space time ripples on 6 June 1907. . But Noble Prize has been given on same illusive theory in 1993 and 2017. Pl read papers published condemning his theory of... more
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GOD - YOU CAN SEE HIM - THE ANU
by MIKE EMERY
THE MALE GOD PARTICLE THAT MAKES EVERYTHING THAT YOU SEE.  AND, AS EVERYBODY KNOWS, MALES ARE A PROBLEM.
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Metal–insulator transition in quantum dot arrays
by David Ferry

2000, Superlattices and Microstructures

Fig. 3. Temperature dependence of the phase coherence time tg for various 2D carrier densities for n-Si-MOS sample 43.
Fig. 9. The effective tunnel oxide thickness, fox, dependence of nm-grain poly-Si thickness.
Table 1: Comparison of different material systems with respect to parameters yielding an rs value of 10.
Fig. 4. Change of resistivity of an n-Si-MOS sample (Si-15A) as a function of the parallel magnetic field for electron various densities at T = 0.3 K.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 7. The breakdown voltage of MOS capacitors dependence on H2O concentration in oxidation and unloading step.
Fig. 3. Theoretical conductance of constrictions Ei, F1 (left) and G1 (right) as a function of the gate voltage.
Fig. 1. Schematic diagram of the multilayer Si quantum dot structure. The inset shows the electron micrograph of the depletion gat« structure for a 200 x 200 nm? dot.
Fig. 3. The peak (solid points) and shoulder (open squares) positions of conductance peaks for various top (inversion) and side (deple tion) gate biases for a 200 x 200 nm2 dot structure.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 2. Single electron oscillations in the quantum dot structure of Fig. 1.
Fig. 1. Resistance-gate voltage characteristic of a quantum dot array composed of three dots with lithographic dimensions of 0.4 x 0.7 wm.
Fig. 3. /-V.q characteristics at Tyyjx = 25 mK under 20 GHz irradiation with different microwave powers at a gate voltage of —200 mV. The curves correspond to microwave power levels of no irradiation (bottom), —40, —37, —35, ~30, —27, —24.5, —22, -19.5, —17, —14.5 and —12 dBm. Inset: differential conductance calculated from the /—V.q data.
Fig. 1. Calculated phonon-induced spin relaxation time 7 in Al as a function of temperature T. Symbols with error bars are experimental data from [5, 19] and the inset is a larger-scale log-log plot. There is good agreement between the theory and the experiment, but the absence of experimental data at temperatures above 100 K makes the calculation a prediction which is particularly useful for spintronic applications at room temperature.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 2. Calculated magnetic field dependence of A, the spin singlet-triplet splitting and B, double occupation probability in the single state for a two-electron double quantum dot. The dot size is 30 nm in radius, and the inter-dot distance 40 nm. There is a single-triple crossing at about 4 Tesla, which is a result of competing Coulomb repulsion, exchange, and single particle kinetic and potential energies DOP is relatively high at low magnetic fields, but is quickly suppressed as magnetic field increases.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 3. Normalized charge conductance G3(eV/A). Curves from top to bottom represent X = 0, 0.1, 0.2. 0.3, 0.4, 0.5, 0.6at Zz =F = 0. The inset shows X = 0.4 results. The upper four curves (from top to bottom at zero bias) have Zg and F values of (0,0), (0.5,0.5), (0.5,0.25), and (0.5,0). For the bottom curve, which corresponds to ky /k,- = 70, the Zs and F values are (0,0). Here the effective masses and the Fermi wave vectors are denoted by m; and kj, where i = 1, 2 correspond to the Sm and S regions, respectively.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 1. Zeeman splitting in ZnBeMnSe in an external magnetic field (left) and possible radiative transitions in GaAs (right). In the ZnBeMnsSe the electrons relax into the lower Zeeman level. In the GaAs the recombination probability with heavy holes is three times as high as for the light hole transition resulting in circularly polarized emission if the electrons are spin polarized.
Fig. 2. Layer sequence (left) and band structure (right) of the spin aligner LED. The device consists of a GaAs/AlGaAs LED which has a spin aligning n-contact. The electrons are aligned in the II-VI layer and recombine in the GaAs with unpolarized holes coming from the GaAs substrate. temperature, a so-called giant Zeeman splitting in the valence band and the conduction band if an external magnetic field is applied (Fig. 1). This large splitting will lead to the relaxation of all conduction electrons into the lower Zeeman level while passing through a ZnMnBeSe layer. Thus, in contrast wit the ferromagnetic metals commonly used as spin injector, our II-VI spin aligner injects a 100% spin-polarized current into the nonmagnetic semiconductor layer. The material can thus be considered as a good candidate for a spin aligner. nonmagnetic semiconductor layer. The material can thus be considered as a good candidate for a spin aligner. We have fabricated several LEDs. All structures consisted of a GaAs/AlGaAs p-i-n diode grown on a p- doped GaAs substrate. On top of the diode, a highly n-doped Zng.91 Beo.o6Mno.03Se spin aligner was grown (Fig. 2). Depending on the thickness of the spin aligner ds, an additional n-doped Zn;—,—yBe,MgySe was added, to obtain an overall thickness of the I-VI layer of 300 nm. This was done in order to achieve identical current spreading in the different devices. The semiconductor layers were grown in in two different MBE chambers for the II-VI and the III-V layers, respectively, and transferred in vacuum. To complete the devices, the structures were covered by a 100 nm Aluminum layer deposited in situ, again without breaking the UHV. After removing the samples from the MBE system, a Mesa was etched and central Al contact pads were fabricated using thermal evaporation, optical lithography and lift-off. The LEDs fabricated this way were bonded and characterized in a He* bath cryostate.
Fig. 3. The degree of circular optical polarization is plotted over the external magnetic field for LEDs with different spin aligners. Thi electroluminescence signal shows a small polarization for dsq_ = 0 (no spin aligner). Be increases with the spin aligner thickness anc saturates for dsq © 100 nm. The PL signal for dsz = 300 nm shows small polarization with opposite handedness originating from thi Zeeman splitting. Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 1. Resistivity versus temperature (from 0.3 to 45 K) for a wide range of density and Fermi energy. Density values are between 0.70 (top) and 35 x 10!! om~2 (bottom).
Fig. 2. Change of resistivity versus magnetic field for n-Si-MOS sample Si-43 at an electron density of 2.6 x 10!2 cm7? at sev- eral temperatures. The dots represent the measurements and the full lines the results of model calculations for the weak localization dependence.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 1. SEM micrograph of the quantum dot array with four dots. The width of the quantum point contacts is 0.15 42m and the lead opening is 0.2 zm. Since the phase-breaking length computed for such a device on the basis of the measured values of the phase-breaking time is larger than its length, we must consider this device as a quantum dot array and not a quantum wire with constrictions.
Fig. 2. Phase-breaking time as a function of lattice and electron temperature with 1/T fits.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 electron scattering at higher gate voltages. At lower gate voltages, there seems to be an error in the fitting a high current values. This might be attributed to the fact that, at low gate voltages, a quantum wire behavior might be more dominant at higher current values, which leads to a T~/3 decay of the phase-breaking time The observed energy relaxation time, as shown in Fig. 3, is much higher than the phase-breaking time, bein; on the order of a few tens of nanoseconds. The power per electron curve shows a break point at about 2.5 K which signifies the onset of a regime where the decay of the energy relaxation time takes place. This woul clearly suggest that the energy relaxation process is not an electron-electron scattering process.
Fig. 3. Energy relaxation time as a function of the electron temperature.
Fig. 1. Schematics of generic open quantum dot devices: single aperture throttle and the double aperture square dot 2. Trajectories and streamlines Previous studies have utilized numerical solutions to the steady state Schrédinger equation for square dots (0.3 zm?) using a self-consistent soft wall model [3]. Here we shall use analytical techniques on hard wall models to extract the underlying physics. The Bohm picture projects the Schrédinger equation for U(x, y) = ./p exp[iS/h] into two real equations: the continuity equation and (for the steady state) the energy conservation equation:
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 2. Upstream and downstream flows in throttle device.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 3. Detail of streamlines in the vicinity of scarring by the classical orbit interfering with the standing wave states showing looping between vortices.
Fig. 4. Construction of vortices and unbounded flow from classical bounce orbits.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 5. Numerical calculation for probability density in a square dot using data from [3]
Fig. 6. Velocity vector field for inset region of Fig. 4.
Fig. 1. A, Resistance of the dot array as the temperature is varied. B, Comparison of the longitudinal magnetoresistance of the dot array and the bare electron gas. Our interest is in the resonances indicated by the arrows. The curve for Vz = —0.55 V has been offset vertically by 100 Ohms.
there is an overall decay with electron temperature, although it is expected to actually be more or less constan below about 1 K, from studies of the zero magnetic field behavior [3]. The magnitude of the relaxation time found here is quite close to the energy-relaxation time determined by a similar process at zero magnetic field While there is certainly some uncertainty in the number of carriers contributing to the resonant peaks (one
Fig. 3. The relaxation time (in seconds) determined from the dependence of the electron temperature on the bias current Fig. 2. The longitudinal resistance for the dot array with Ve = —0.55 V. A, Rxx for several values of the lattice temperature. The upper two curves have been offset by 2000 and 4000 Ohms, respectively, for clarity. B, Rxx for several values of the current through the array. The upper two curves have been offset by 2000 and 4000 Ohms, respectively, for clarity.
Fig. 1. A, Geometry of one of the inhomogeneous magnetic confining fields used in our simulations, here forming a semicircular quantum dot. B, The first 25 eigenstates of the semicircular dot, given B = 307 Bg. What is plotted is the magnitude of the wavefunction versus x and y.
Fig. 2. Here, A-F correspond to six different orbits supported by this structure, given a cyclotron radius of ~0.05a Several of the eigenstates shown here obviously correspond to edge states that travel along the outer edge of the entire boundary. However, some of the states show rather interesting behavior in the interior. For example, states 7 ‘and 15 have a distinct ‘V’ form, while state 10 looks somewhat like a ‘fan’. State 11 has edge state-like properties, however, its amplitude is concentrated mainly along the circular boundary. State 12 has an ‘A’ pattern to it, while states 21 and 22 show very complicated interior patterns that create a low amplitude spot on the center of the right side. State 20 shows a similar pattern apparently coexisting with an edge state. To get some insight into the physics of this structure, we have also performed classical simulations, finding many of the periodic orbits or closed trajectories allowed by its geometry. Several examples are shown in Fig. 2. Figure 2A shows a ‘whispering gallery’-type orbit that follows the left circular boundary while simply bouncing off the right barrier. In Fig. 2B, we show an example of a “V’-type orbit. In Fig. 2C is a more complicated but closely related orbit (obtained using slightly different initial conditions) that is in the form of a ‘fan’. Figure 2D shows an orbit that has an ‘A’ pattern. Figure 2E shows a rather complicated orbit that does not visit a spot on the center of the right boundary. The orbit in Fig. 2E has a similar ‘blind’ spot, but spends much of its time on a path that follows the entire perimeter of the dot. There is a resemblance between the patterns revealed by these orbits and several of the eigenstates pointed above. We believe that many of these eigenstates are in fact ‘scarred’ by these orbits, or at least orbits that belong to the same or similar
Fig. 3. A, The first 25 eigenstates of the stadium, with a middle section a/6 units long. Here, B = 350 By. B, The first 25 eigenstates of a square with B = 303 Ba, a is now the side of the square.
Fig. 1. A, Geometry of the split-gate quantum dot array that is simulated. B, G of the array versus Fermi energy, E, for s = 0.1 um, W = 18 meV (lower curve) and s = 0.15 um, W = 4 meV (upper curve). C, G versus E for a 0.4 zm dot with soft boundaries as depicted in the inset.
Fig. 2. A, G versus 1/T for the array with Ey = 15.245 meV (solid line). The dashed line is a fit to eqn (1) with Gg = 0.02 e*/h, G, =0, Gz = 0.28 e*/h, To = 0.13 K, and p = 1.25. B, G versus 1/T for the array with Er = 15.633 meV (solid line). The dashed line is a fit using Go = 0.986 e2/h, G1 = 0, Gz = 0.88 e2/h, To = 0.47 K, and p = 1.2. C, G versus 1/T for the soft dot with Ep = 17.55 meV (solid line). The dashed line is a fit using Gg = 3.576 e?/h, Gy =0, Gz =2.2 e2/h, To = 0.52 K, and p = 1.1.
Fig. 3. A, Normalized conductance versus 1/7 using the two resonance model (solid line). The dashed line is a fit to eqn (1) with Go = G, = 0, G2 = 1.1, To = 0.54 K, and p = 2.4. Inset: the two transmission resonances, with the line in between indicating Ey = 15.7 eV.B, G versus 1/T using eqn (1) with Go = 2.2 e*/h, Gy = 0.13 e2/h, Gp = 0.90 e2/h, Ty = 0.54 K, and p = 2.4. The dashed line was obtained by scaling the curve in A by a factor of 0.81 and adding Gg = 2.2 e?/h as well as a In(T) term with prefactor G; = 0.13 e*/h.
Fig. 1. The conductance through the anti-dot array as a function of the magnetic field normal to the two-dimensional plane of the | pm? square active area. The number of anti-dots in the active area is indicated by the label of each panel. The solid curves are for hardwall boundary conditions, while the dotted curves are for periodic boundary conditions.
Fig. 2. Variation of the conductance as the Fermi energy (density) is varied in the anti-dot array.
Fig. 1. The main velocity flow processes in a square quantum dot include open orbits which directly traverse the dot, and long meanderin open orbits which thread through clusters of localized vortex flows [1].
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 2. New singularities in the velocity flow resulting from the nonHermitian Hamiltonian model. The case shown corresponds to a source and sink pair which model the scattering of a particle with consequent energy and momentum gain or loss.
Fig. 3. Frames from a simulation of the time evolution of a Gaussian wave packet injected into a single transverse mode of a throttl device in 2D showing the probability density landscape as a function of time using the fast algorithm described in the text.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 1. Far-infrared absorption of a vertically aligned dot array. Two broad peaks (peaks | and 3) shift toward higher magnetic field wit the angle of the magnetic field. The inset shows the schematic cross-section of a sample.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 3. Modulated absorption signal under bandgap excitation. At the position of peak 1, the characteristics change due to peak shi being recognized. Fig. 2. Magnetic field dependence of the peak position and calculated magnetic dispersion curves for several values of wo. Experimenta data can be well fitted with the curves for 1 and 3 meV of wo.
rest of the cell, whose area fluctuates independently of that of the hole relative to the dot being considered. The second set of samples is a similar dot array of 40 holes, whose area has an average of 6520 nm? and a standard deviation of 295 nm?.
Fig. 2. Ground-state energy versus inverse area for single dots (full circles) and for dots in a cell (open circles), relative to the sample shown in Fig. 1.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 3. Ground-state energy versus inverse area of for the dots in a cell with a pitch of 100 nm (open circles), for the dots in a cell with a pitch of 200 nm (full circles), and for single dots (full squares), relative to the second hole-array sample.
Fig. 1. SEM photograph of the multi-quantum dot sample and a schematic diagram of the configuration of quantum dots and split gates. The series-coupled sample of dot 1 and 2 and source 1 and drain | were used in the present experiment with the third dot cut-off by the split gate.
Fig. 2. Gray-scale plots of source current J, at drain voltage Vqg = 100 mV as a function of Vcg; and Veg for three different interdot couplings controlled by Vpg2; A, Vpg2 = —1.22 V, B, Vpg2 = —1.215 V and C, Vpg2 = —1.205 V. On the interdot conductance, see the text. Some tetragons shown by solid white lines as a guide for the eye in A mark regions where a particular configuration of excess electrons in the dot system is stable and there is no charge transport due to the CB.
Fig. 3. A, Source current /; versus drain voltage Vy characteristics of double dots as a function of gate voltage Vy for the intermediate interdot coupling (Fig. 2B) and B, the gray-scale representation of /, on the Vg-Ve plane.
Fig. 4. A, Source current /, versus drain voltage Vg characteristics of a double dot with a weak coupling as a function of gate voltage at higher drain bias and B, the gray-scale representation of /, on the Va—Ve plane.
Fig. 1. SEM photographs of the split gate structures El, Fl, and G1.
voltage of the split gates. In this paper, we focus on the split gate structures, and, among the full gates, we consider only the one with the largest width, whose pinch-off value should be essentially equal to that due to an infinite metal plane at the surface of the heterostructure.
Fig, 2. A, Electron density in the 2DEG as a function of Epin; B, electron density as a function of the gate voltage for different etching depths (nm) with Epin = 0.74.
Fig. 1. A, Schematic representation of the Si quantum dot. B, SEM micrograph of the depletion gate pattern Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 2. Energy spectrum versus applied depletion gate voltage. The top gate voltage is fixed at A, 8 V and B, 7 V.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 3. A, Top view of the conduction band edge. B, Electron density in the plane parallel to the semiconductor—oxide interface
On the top right panel, the magnitude squared of the expansion coefficients (|Cy|”) versus the eigenvalue number for this particular state is shown. We use as a complete orthonormal basis set the wavefunctions calculated when using uniform impurity distribution. It is quite clear that atomistic impurity distribution, which introduces random fluctuations in the confining potential, leads to mixing of the states. In the bottom panel of Fig. 5 we show the basis functions corresponding to the fourth, fifth and sixth eigenstate which contribute to the mixed state shown in the top left panel. In conclusion, we have presented simulation results for the energy level spectrum in quantum dots operat- ing in the tunneling regime. We also identified the experimentally observed conductance peaks with energy level in the dot crossing the Fermi level. Examining the influence of atomistic doping description we found out that uniform doping distribution leads to well-defined wavefunctions, and that it is not hard to establish one-to-one correspondence between a wavefunction and a given eigenstate. In the discrete impurity distribu- tion case. mode mixing of the wavefunctions was observed.
Fig. 5. Wavefunction in the top left, obtained through discrete impurity simulation is a mixed mode consisting of three other modes shown in the lower part of the figure. On the top right panel the magnitude squared of the expansion coefficients ({Cy|2) versus eigenvalue number for this particular state is shown.
Fig. 1. Oxide thickness as a function of etching time in a 0.1% HF solution. The oxides grown on Si(11!) and Si(100) were simul- taneously etched in the same HF solution. The oxide thickness uniformity was confirmed by AFM at representative steps of oxide stripping. Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 3. 0}, photoelectron and its energy loss spectra for oxides grown on Si(100) at 1000 °C.
Fig. 4. Tunnel current through ultrathin oxides for n*-poly-Si gate MOS diodes measured as a function of voltage across the oxide. The tunneling effective mass ma == 0.35mg and the oxide conduction band effective mass m%, = 0.60mg are used in the calculation.
Fig. 5. Measured and calculated direct tunnel current densities through 1.65-3.90 nm thick oxides as a function of oxide voltage.
Fig. 6. Relationship between linear mode Vi, and J, distribution at Vg = 1.5 V or at Vi, for A, 1.2 nm and B, 2.0 nm gate oxide MOSFETs.
Fig. 7. Schematic explanation of Vip fluctuation induced by /y distribution. Equivalent circuit of Jy path A, and Vin shift or fluctuation AVin caused by /g variation B.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 8. Relationship between oxide resistance Rsio, and oxide thickness. Rgi9, was obtained by Eox Tox divided by Ig while Rsion for Ref. [1] was evaluated by Vg(= 1.5 V) divided by Jz. — Calculated by MST, Eox = 5.0 MV cm7!, @, this work MOSFET, Eox = 5.0 MV cm7!; a, this work MOS diode, Eox = 5.0 MV cm7!; 0, MOS diode, Vz = 1.5 V [1]; A, MOS diode, Eox = 5.0MV cm! [2].
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 9. Drain current-gate voltage characteristics of a Si QD floating gate MOSFET. The gate length and width are 0.5 zm and 10 pm respectively.
Fig. 10. Minimum drain current as a function of the gate voltage.
Fig. 11. C-V characteristics of a Si QD floating gate MOS capacitor. The steady state C-V curves were obtained from the transien response under constant bias. Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 14. /g-Vg curves for a 26 nm gate length MOSFET. Fig. 13. Cross-sectional SEM image for 30 nm gate pattern.
Fig. 12. SiO. gate mask shrinking rate versus etching time. Here, Ljpj is the initial gate length and Lorch is the gate length after shrinking Solid circles and open squares refer to different runs.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 1. The closed wet cleaning (CWC) system. Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 4. A, Process sequence for a nm-grain/large-grain double-layer poly-Si gate. B, TEM observation of a nm-grain/large-grain double- layer poly-Si gate. 2.4. Electrical measurement
Fig. 2. The load-lock oxidation system. Fig, 3. Oxidation sequences in the load-lock oxidation system.
Fig. 5. Comparison of FT-IR/ATR spectra obtained from Si surfaces with different surface treatments. One is after conventional we station cleaning (Conv.) and the other is after H termination in the closed wet cleaning (CWC) system.
Fig. 6. J—V characteristics of MOS capacitors with thin gate oxides. Gate oxidation processes were performed after conventional pre-cleaning in wet station (Conv.) or H termination with closed wet cleaning system (CWC).
Fig. 8. Predicted gate oxide yield in LSI chip after 10 years of operation under 4 MV cm7! and 5 MV cm! oxide field
calculated weak spot densities in gate oxide formed by various techniques, we predicted the reliability of the gate oxide from the combination of CWC and WODU as functions of total gate area and operating electric fields. Figure 8 shows the results which indicate that the CWC and WODU technique significantly improved oxide reliability, showatg that a 90% yield is expected after 10 years of operation, even when the total gate area is'as large as 1 cm? and the electric field is as high as 5 MV cm— I E. The gate poly-Si structure impacts on oxide reliability
Fig. 11. F—N plot of MOS capacitors with a nm-grain poly-Si gate. The ratio By/B represents the local field enhancement factor
Fig. 12. AFM image of the tunnel oxide surface after poly-Si gate removal by N2Hq etching. A, without a nm-grain poly-Si layer B, with a nm-grain poly-Si layer when the thickness is 4 nm.
Fig. 13. Constant current TDDB measurement results for MOS capacitors with a nm-grain poly-Si double-layer gate. FE. High-k gate dielectric films
Fig. 1. Schematic views of the lowest conduction bands of Si and SiOz, projected on an axis through ky = 0 that points in the [010] (or, equivalently, in the [001]) direction. The SiOz bands are shifted relative to the Si bands by the conduction band offset Ecgg. A, Effective-mass picture B, tight-binding picture for the 2 x 2 structure studied here: the bulk Si bands are folded in the 2 x 2 Brillouin zone; the cross and circle indicate regions where electrons from different valleys couple. C, is the same as B, but outfolded back in a 1x 1 cell.
Fig. 2. Transmission coefficients T(E, k|, = 0) for incident electron energies E of: A, 0.02 eV, B, 1.0 eV, and C, 2.0 eV as a function of applied voltage, obtained within the present tight-binding (solid lines) and the effective-mass (dashed lines) methods for various oxide thicknesses d. Note that the B and C depict the sums of the TB transmission coefficients of all six and ten incoming states, respectively.
Fig. 1. Relative RTS amplitude associated with the trapping of a single electron in the middle of the channel of a 100 x 100 nm MOSFI as a function of the drain current. Vp = 10 mV. Fig. 2. Dependence of the relative RTS amplitude on the gate voltage for a set of square decanano MOSFETs. Vp = 10 mV. very broad, weak maximum before rolling-off in strong inversion. The 100 x 100 nm MOSFET, due two generations from now, is the starting point of our investigations. The RTS amplitude for this device already reaches 5% in weak inversion but falls to a fraction of this percentage at large gate voltage. For the whole range of investigated square devices, the relative RTS amplitude remains inversely proportional to the channel area. For the 30 x 30 nm MOSFET, which marks the end of the roadmap, the RTS amplitude increases to more than 40% in weak inversion and remains above 5% for the whole range of gate voltage relevant to this generation of devices. i - oa 7 Py ve: Pe 2 to 2 tot
Fig. 3. Relative RTS amplitude as a function of the relative position of the trapped electron moving from the middle of the channel to the source.
Fig. 4, A, Gate voltage dependence of the largest relative RTS amplitude in a 50 x 50 nm MOSFET with random doping and the highest relative RTS amplitude in a device with continuous doping; B, the same as A but with the two curves aligned in respect of the threshold voltage. a dominant current path and can introduce RTS with a much larger amplitude than the maximum amplitude deduced from continuous doping simulations. In this section we present results from a full-scale atomistic simulation where not only the trapped electron charge but also the acceptors in the channel are represented as random discrete charges. The discrete random dopants are introduced only in the channel region between the source and drain with continuous doping assumed in the source and drain. The average number of dopants in these regions are calculated by multiplying the volume of the random dopant region by the corresponding doping concentrations. The actual number of dopants in each atomistic region is chosen randomly from a Poisson distribution with a mean equal to the corresponding average dopant numbers.
Fig. 1. Comparison of the CA method with EMC for Si at 7 = 300 K for the A, the drift velocity and B, the average energy vs. field.
Fig. 2. Three-dimensional schematic layout for a 50 nm n-channel MOSFET.
Fig. 3. A, J-V characteristics for MOSFET structure using the 2D Poisson solver. B, Potential profile using the 3D hybrid CA/multigri algorithm for Vg = 2.88 V and Vg = 2.0 V. When used in this hybrid mode, the simulator can adaptively update the transition/scattering tables to account for changes in the location of high scattering regions. aa — — _— In the present work, acoustic phonons, nonpolar optical phonons and ionized impurity scattering are in- cluded. The models used are essentially identical to those used in Fischetti and Laux [4], in order to compare the results for the full-band CA (see Fig. 1). Impact ionization is also included with a separate algorithm due to the multi-particle nature of this mechanism. The energy-dispersion relation and the phonon spectra are calculated across the entire Brillouin zone using an inhomogeneous grid. Due to symmetry, only values in the irreducible wedge of the first Brillouin zone actually need to be determined and stored. The band structure is calculated using the nonlocal empirical pseudopotential method (EPM) [5] including spin-orbit interaction, and the phonon dispersion is calculated using an empirical shell model [6]. Both electrons and holes are simulated.
Fig. 1. The calculated resistivities for various electron densities, ns = 1.03, 1.08, 1.19, 1.31 x 10!! em-2 (top to bottom) as a function of T for the Si-12 sample of Ref. [1], using the critical density np = 10!! cm7?. In the inset we show the analytic zero-temperature conductivity as a function of density 1. Points represent extrapolated o(7 — 0) from Si-12 sample of Ref. [1].
Fig. 1. Ratio of energy relaxation rates to bulk values vs. temperature for a semiconductor bounded by a vacuum (a metal film). The distance zg from the crystal surface to the center of a QW equals 3d/2, where d is the width of the well. Sheet electron concentrations ns are: 1-10!! em=?; 2, 4, 5-2.2 x 10!! em7?; 3-3 x 10!! cm=?; well widths, d: 1, 2, 3-50 A, 4-40 A, 5-100 A. The curves marked by a circle in the upper part of the figure correspond to a semiconductor in contact with a metal film. The transition probability due to the interaction with phonons is calculated within the fermi golden rule approximation. Further derivation of the total relaxation rate may be carried out in analogy to that for DP scattering [3]; the procedure yields the following final form
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 2. Ratio of energy relaxation rates to bulk values as a function of distance from the crystal surface to the center of QW, Z = 2zq/d, for a semiconductor in contact with a vacuum (a metal film) at temperature T = 0.2 K. The electron sheet concentrations ns = 10!! cm=2; well widths d: 1-40 A, 2-50 A, 3-100 A. The right y-axis refers to a semiconductor in contact with a metal film.
Fig. 3. Energy relaxation rates as a function of temperature for a semiconductor in contact with: 2: a vacuum, 3: metal film. Curve 1 corresponds to a bulk rate. Sheet electron concentration ns = 2.2 x 10!! cm~2, well width of 40 A.
Fig. 1. C-V depth profiles of the active Si donor concentration for hydrogenated (H) or deuterated (D) Schottky diodes. -e-e, Hydro- genated diode after plasma exposure and before annealing or bias stress (the results obtained for deuterated samples are very close to those obtained for hydrogenated samples). —, Hydrogenated or deuterated diodes simultaneously annealed without bias at 250°C for 1 h. —-, Hydrogenated or deuterated diodes submitted at room temperature to bias stress at a reverse voltage of 5.5 V. The bias stress time (about 5 h) have been selected for H and D samples to have the same given electron number Ne = 16.7 x 1018 injected in the diodes.
Fig. 2. Evolution of the sheet carrier concentration (full line) and of the electron mobility (dashed line) measured by the Hall effect on hydrogenated n-type Si-doped GaAs epilayer versus the electron number dose for various electron injection energies : 10 (Ml), 20 (4) and 30 keV (@). scanning electronic microscope (SEM) or an electron lithography system. Such a method has already been used for acceptors reactivation in Mg-doped GaN [6]. To test this possibility in the case of Si- doped GaAs, experiments have been carried out on 0.35 wm thick Si-doped epilayers grown by molecular-beam epitaxy. From the Hall measurement, sheet electron concentration N, = 1.4 x 10!4 cm™~? and free carrier mobility pun = 1690 cm? V s~! have been obtained. The layers are then exposed to a RF plasma under the following conditions: temperature of 190°C, hydrogen pressure of 1 mbar, RF power of 0.16 W cm~? for 8 h. After plasma exposure, the samples are characterized for Ns = 4.6 x 10!? cm? and un = 3550 cm? Vs7!. These results can be explained by the neutralization of ionized donors, and the increase of mobility is due to he decrease of ionized impurity scatterings. Then, we have exposed the whole clover surface to the focused electron beam of a SEM with different electron injection energies: 10, 20 and 30 keV. The obtained results for an increasing incident electron number are presented in Fig. 2.
Fig. 3. CL image of the laboratory logo written with a 20 keV electron beam on hydrogenated Si-doped GaAs sample. The electron dose is 0.5 C cm, The CL reading of the patterns has been made on a sample cooled down to liquid nitrogen and the CL signal has been collected by an ellipsoidal mirror of an Oxford system mounted on the scanning microscope.
Fig. 1. Hydrogen formation energies as a function of the electronic Fermi energy of A, silicon and B, silicon-dioxide. The valence band maximum determines the zero of energy for both plots. Comparing A, with B, we note that neutral hydrogen will favor the silicon over the silicon-dioxide interface. In A, notice that hydrogen can lower its formation energy by becoming charged and the transition from positively to negatively charged is just below 0.8 eV. This transition for bulk silicon and is also observed at the Si-SiO} interface of MOSFETs during hot electron stress.
Fig. 1. Illumination wavelength dependence of the extra sheet carrier concentration resulting from the light-induced Si-H complex dissociation in n-GaAs (3 h light exposure): @, YAG or Ti-sapphire laser illumination; LJ, monochromatic radiation provided by a UV spectrometer (power density: 1 mW cm72),
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Fig. 2. Evolution of the Hall electron mobility with the Hall carrier concentration resulting from the two parallel conduction paths, the passivated region and the region reactivated by UV illumination: @ (H) and O (D), before passivation; ¥ (H) and V (D), after passivation; Ml (H) and by UV illumination. (D), after passivation and chemical etching; 4 (H) and A (D), after passivation and chemical etching followed
Fig. 3. Photon density dependence of the extra sheet carrier concentration for a hydrogenated and deuterated structure at 300 K anc 100 K. The UV illumination comes from the 350 nm emission of an argon laser.
Fig. 1. A, Schematic picture of the device layout (not to scale). The lower part of the figure symbolizes the current path for reverse bias in a situation where the top (TG) and bottom (BG) gates have pinched off the electron gases at their respective positions. B, Conduction band profile and self-consistently calculated energy levels of the tunneling structure used to demonstrate the present device principle. The shaded region indicates the 5-doping of the barrier.
Fig. 2. Differential conductance d//dV,, measured at T = 1.9 K for various values of Vcg (from top to bottom: Veg = —0.6, —0.65, —0.7, —0.75, —0.8, —0.85, —0.9, —1.0 V). Curves are vertically offset. The right inset shows the differential conduc- tance dI/dV, for the 2D-2D case at Vcg = 0 V. The left inset symbolizes the top view of the device. Gated (g) and ungated (u) regions of the device lead to different parts of the tunneling spectra as described in the text.
Fig. 3. A, /—V plots for initial and subsequent positive and negative biasing at 4.2 K. B, J-V plots after biasing with increasingly negative voltage (+10, —1, —2, —3, —5, —10 from right to left) at 4.2 K.
Fig. 3. A, Differential conductance corresponding to Vcg = 0 V and —0.8 V, recorded in a magnetic field parallel to the tunnelin: current with field strength of 5 T. B, Calculated DTC for a magnetic field of 5 T. Downward arrows indicate the various transition between Landau levels that have been taken into account in the calculation. The notation i — j® means a transition from the ith LI in the InGaAs well into the jth LL of the kth subband of the GaAs—AlGaAs junction. The upward arrow indicates the voltage positio of the first 2D-2D resonance without magnetic field. Note that here d//dV,* is plotted against the voltage drop across the tunnelin barrier V;*.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 4. Subband spacing of the lower channel as a function of the central gate voltage. Solid and open symbols were obtained from different pairs of peaks of the 1D-1D tunneling characteristics shown in Fig. 2. The solid line is a quadratic fit to the data and serves as a guideline to the eye.
Measurements in nonzero magnetic fields The following gives a brief account of the results obtained when a magnetic field is applied parallel or perpendicular to the direction of the tunneling current. Both types of experiment give additional evidence that the structure observed in the dI /dV} curves, when the central gate is negatively biased, in indeed due to tunneling between 1D states. Figure 6 shows how the peak positions of the 1D-1D tunneling structure in Fig. 2 evolve with a magnetic field applied parallel to the tunnel current. The central gate voltage in this case was Vcg = —0.8 V. An example of typical d//dVp trace at B = 5 T is shown in Fig. 3A. As can be seen in this figure, there is no significant change in the qualitative features of the respective tunneling characteristics. Figure 6 shows moreover that even in the peak positions no significant change occurs as long as the magnetic field strength is smaller than 3 T. This is exactly what one expects, if the tunneling indeed occurs between 1D levels. A magnetic field perpendicular to the sample surface leads to a B-dependent subband spacing according to ha = (hwo)? + (hw-)2, where w, denotes the cyclotron frequency and wo is the spacing of the 1D sub- bands without magnetic field. At low magnetic fields the electrostatic confinement (characterized by wo) con- sequently dominates the additional confinement introduced by the magnetic field, whereas at high B-values the opposite is true. As already discussed by Mori et al. [11, 14], in the first case tunneling occurs between 1D states of equal parity, in the second case mainly between magnetoelectric hybrid (Landau) levels of identical LL index. There should therefore occur a crossover between the two cases when the magnetic confinement begins to dominate over the electrostatic one. One expects additional peaks beyond this crossover, since tun- neling is now also allowed between magnetoelectric hybrid levels of the same index. As seen in Fig. 6, there is indeed some evidence of such a crossover between 2.5 and 3.5 T. At lower magnetic fields the peak po-
Fig. 6. Peak positions of the 1D-1D resonant structure in the differential conductance obtained for the device with 1 zm channel width and plotted versus magnetic field strength. The orientation of the magnetic field with respect to the device geometry is drawn in the inset. The peak positions are directly obtained from the d//dV, traces without re-scaling the bias voltage axis.
the behaviour of the gross structure of the tunneling characteristics, which according to the model of Mori et al. [11] should indeed give almost identical results for both magnetic field directions. Summary The above considerations demonstrate that the side-gate technique indeed gives a simple and flexible possibility to implement both a selective depletion scheme and a lateral confinement which is very effectively tuned by the voltage applied to the central gate. The tuning range of the 1D sublevel spacing has been found to lie between effectively 0 and about 6 meV, allowing the study of 2D-2D and 1D-1D tunneling processes on one single device. The above selective depletion scheme can be applied to a variety of mesa geometries and is not restricted to two-terminal configurations. The only essential prerequite for the introduced side-gate technique is to have sufficiently different carrier densities in the two barrier-separated electron gases. Our results also show that the use of gate-tunable etched quantum wire structures allows us to obtain 1D subband energies, which are indeed in a range interesting for the application of quantum wires as detecting devices
Fig. 1. A, Schematic of experimental geometry for magnetoconductance measurement. B, Split gate geometry. C, Scanning electron micrograph of a test structure. The actual sample was only 3000 A thick, so that the front and back split gates were of equal distance from the electron layers.
Fig. 3. Waterfall plot of conductance G versus Vp and Vg shows uniform quantized conductance steps for regime (iv), where only one 1D wire is present. A complex interference of the steps is evident in regime (iii), where both 1D wires are occupied. Fig. 2. Sample resistance versus Vp with Vg = 0. Inset at bottom shows transition from regime (i) to (ii) at Vy = —0.3 V. The transition from regimes (ii) to (iii) can be seen at Vp = —0.7 V while a distinct increase in slope at Vy = —2.6 V marks the transition from (iii) to (iv). plot. However, when both wires are occupied (regime iii), quantized steps are again present, but form a complicated interference pattern. By tracking the position of individual conductance steps as a function of both Vy and Vp, each step can be assigned to one quantum wire or the other. Clearly, each QPC width—and thus the number of occupied subbands—can be independently controlled by the action of Vp and Vz. LM ERM RMR: a EL RE N,N ee , ae e ee eeeNNee meee: Rk emer: eee We now turn to the behavior of the conductance under an in-plane magnetic field B applied perpendicular to the direction of current flow. Figure 4 shows a contour plot of the logarithmic derivative of the resistance d[In(R)]/dVz, as a function of Vp and Vg. The different regimes are again readily identifiable. Insets (a)—(e) show G versus B taken at several different values of Vr and Vg. Inset (a) was taken at Vp = —0.25 V and Vg = 0.0 V. The familiar 2D-2D anticrossing features, a conductance peak followed by a shallow dip, are centered about B = 6.5 T. This is consistent with the sample being in regime (i) [6].
Fig. 4. Contour plot of the logarithmic derivative of the resistance A[In(R)]/0Vy. The different regimes are readily identifiable. Insets (a)-(e) are plots of G versus B taken at the indicated values of Vp and Vg. Here, where the in-plane B is perpendicular to the current direction, a broad conductance dip develops in regime (iii).
Fig. 5. Contour plot of the logarithmic derivative of the resistance d[In(R)]/8Vy, where again insets (a)-(e) are plots of G versus B taken at the indicated values of Vr and Vg. Here the in-plane B is oriented parallel to the current direction, and no broad conductance dip is seen to develop.
Fig. 6. Sketch of the dispersion curves for a symmetric pair of coupled double quantum wires, for the case where the subband spacing is much smaller than Agag. The in-plane magnetic field is applied perpendicular to the current direction. A, B = 0. B, B = 6.5 T. C, B =~ 12T.
Fig. 1. Confinement without walls in metal-clad InAs structures.
Fig. 2. Absorption spectrum of the Al-clad InAs structure. A and B show the intersubband absorption of the same sample before (A) InAs quantum states are confined by AlSb barriers and after (B), processing the sample to the Al-InAs structure. and a well-width fluctuation induced by the process and/or by reaction of Al with InAs [6]. The data suggest that despite the expected transmissivity of the Al-InAs interface, the electrons are strongly reflected either by band structure discontinuity or formation of a AlAs barrier. In Fig. 3, we show the absorption of a W—InAs quantum well compared with the barrier bound system. The process followed the Ai-InAs quantum well shown in Fig. 2. We found that W—InAs exhibits intersubband absorption, shifted toward higher energy and broadened, showing that the W-InAs interface is also reflective in a way somewhat similarly to Al-InAs. The amount of peak shift, 26.1 meV, is of the same order as the shift in Al-InAs. However, W—InAs shows an anomalous absorption in the lower energy side of the original intersubband peak which is not observed in the Al-InAs structure. The width increase Aw = 67.1 meV is more than factor of 2 of A,4;. This anomalous absorption cannot be accounted for by well-width fluctuation. Similar anomalous low-frequency absorption is also observed in structures using Pt, Ag, In, Au, Nb, and Ti. Nearly same peak shift of both Al-InAs and W-InAs indicates that the effect of the etching and Ar plasm
Fig. 3. Absorption spectrum of the W-clad InAs structure. A and B show the intersubband absorption of the same sample before (A) InAs quantum states are confined by AJSb barriers and after (B), processing the sample to the W-InAs structure.
Fig. 1. A basic quad-element derived from an EEPROM device with self-assembled nano-crystal floating gate. Notice that the nano- crystals do not need to be evenly distributed for the four-quadrant applications. They only need to be small enough to take advantage of the Coulomb blockade effect.
Fig. 2. Size distribution of the self-assembled dots and its relations with the lithography process. Notice that the layer thickness depen dence has not been taken into consideration.
Fig. 3. Self-assembled Au dots on adjacent oxide and Cr regions. The direct comparison can isolate the thermal effects and offe information on formation energy and effects of surface roughness. Fig. 4. Self-assembled Au dots on smooth oxide with E-beam-prescribed Cr arrays. This hybrid process can be used to characterize self-assembly forces since Cr has much smaller surface mobility than Au and serves as place-holders. functional density is only comparable to CMOS, then the SA process can only enhance structural stability. This leaves a small window of functional density of the SA structures if interface with CMOS circuitry is necessary. The number of zones of nano-crystals floating gates associated with electronic functions in the proposed nano-crystal EEPROM cell is hence quite limited, unless direct information access can be provided from the third dimension as in the tera-bit storage case [4]. Another possible way to surpass the Rent’s limit is by considering that the electronic functions are very different in nature than logic circuits, as in the case of electronic synapse [1]. This, however, implies a complete change in processing architecture. If only four
Fig. 5. Simulated channel electron concentration under a split-gate MOSFET. The two gates can be easily distinguished by DIBL asymmetry.
Fig. 6. To write an individual dot using the peripheral contacts, two corner contacts are fully biased, while the other two half biased or floating.
Fig. 8. Demonstration of process flow for the nano-crystal floating gate device. Notice that this flow is for illustration purposes only. The geometry is not drawn to scale. ure 5 shows the simulated channel carrier concentration in a 50 nm split-gate MOSFET using a conventional drift-diffusion model, where DIBL asymmetry is indeed significant. Programming of each individual zone can be achieved through hot-carrier injection with the bias condition shown in Fig. 6. Erasing all four nodes can be achieved by tunneling through the control gate. This is similar to the popular FLASH operations [6].
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 7. Equivalent circuit of the electron synapse with output set by the convolution of the channel current history stored in nano-crystal floating gates.
Fig. 9. Preliminary measurement of the Au nano-crystal EEPROM cell. The drain bias is 5 V. The solid line has control-gate bias at —5 V, the short-dashed line has 0 V and the Jong-dashed line has 5 V. The drain current is tuned by the floating charge in the nano-crystals injected by hot channel carriers. Leakage is almost negligible with no control gate bias. Hot carrier charging is self-limited.
Fig. 1. TMAFM analysis of exposed 10-undecenoic acid features as a function of dose.
Fig. 2. A, Capacitance versus frequency for metal-oxide-SAM-metal structures without electron-beam lithography exposure. The capac- itance is taken from the average capacitance over one period. B, Capacitance versus voltage over one period at 100 kHz and 1 MHz for an exposed metal-oxide-SAM-—metal structure. Four measurements at each frequency are shown each fitted to a Boltzmann distribution.
thus the capacitance of the SAM can be measured directly. We assume that the capacitance of the SiO? layer is not affected by the addition of the SAM. Figure 2B shows the capacitance of the SAM versus voltage over a single period at 100 kHz and 1 MHz, the data are well fitted by a Boltzmann distribution.
Fig. 3. A, Equivalent model circuit for the SAM. Cconst is the constant capacitance and +o/—o denote the location of the effective bound charge due to the intrinsic polarization of the SAM. B, Values of the constant capacitance of the SAM and voltage dependent capacitance, due to the intrinsic polarization of the SAM, versus frequency for SAMs with and without electron-beam lithography processing.
Fig. 2. A, Electron micrograph of dendritic electrodeposit which has been broken to form isolated silver islands (the anode is on the far left). B, /-V plot of device at 4.2 K (the solid curve is a guide for the eye). Fig. 1. A, Top view schematic of coplanar electrode device. B, Solid solution in via between electrodes.
Fig. 4. Field emission scanning electron micrograph of solid solution in a 50 nm wide via in SizNq on an underlying silver electrode
Fig. 1. A, The /-V characteristic of a poly-L-lysine-nanoparticle sample. B, The /—V data after subtraction of the background conduc- tance of the undecorated biopolymer.
Fig. 3. A, Monte Carlo simulations of chains of one (— e —), two (— —) and five (——) nanoclusters in series. B, Monte Carlo simulations of five nanoclusters in series with 420% ( ) and 467% (— —,) variation in nanocluster radius. All simulations were done for a temperature T = 300 K.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 1. Scaled current—voltage characteristic for an SSL with wo (ye /Y¥vz)'/ 2—=-landC =0 (A), C = yyz (B) and C = 15yyz (C).
Fig. 2. Scaled current-voltage characteristic for hot electrons in an SSL with wo(ye /Yuz)!! 2—05andC = Yuz (A), and C = S5yyz (B).
Fig. 2. Electron dephasing rate due to transverse phonons in Al structures with electron mean-free path / = 0.005 jm and 0.05 ym. Solid lines correspond to complete drag of all scatterers (boundaries and impurities) by phonons. Dashed and dotted lines correspond to the electron mean-free path with respect to the static potential L = 0.05 xm and 0.5 um.
Fig. 3. Dependence of the dephasing rate on the electron mean-free path. Solid and dotted lines represent contributions of longitudinal and transverse phonons, correspondingly.
Fig. 1. Impurity scattering time, timp, as a function of applied voltage, V, for A, 5-doped triple quantum wells and B, 6-doped double quantum wells. The areal donor density in Ng = 2 x 10!2 cm7?. Solid lines (dashed lines) represent Timp from the ground subband in the narrow well to the ground (first excited) subband in the wide well. The insets show a self-consistent electronic states at V = ~3 V.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 3. Temporal variation of photoluminescence intensity for the narrow well of 5-doped triple quantum well samples with differen 5-doping densities. Fig. 2. Photoluminescence decay time from the narrow well in the undoped double quantum wells (DQW) (open triangles), the 5-doped DQW (closed triangles), the undoped triple quantum wells (TQW) (open circles) and the 6-doped TQW (closed circles) as a function of applied bias voltage from —3.5 to +1.0 V with a 0.1 V step at 10 K.
Fig. 1. Chopped quantum well with calculated electron and hole envelope functions (interface layers not shown).
Fig. 2. Calculated TE and TM absorption spectra (300 K) for the 0.85% tensile-strained sample. The inset shows the calculated elec trorefraction.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 3. Calculated optical path length difference due to the QCSE and the Pockels effect for TE and TM polarization for the 0.85% tensile-strained sample at 1530 nm.
Fig. 4. Measured polarization-independent switching in a MZI using a 4 mm phase shifter with —0.85% strained chopped quantum wells (vertically scaled, see text).
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 5. Measured optical path length difference due to the QCSE for different operating wavelengths for the —0.65% strained CQW
Fig. 6. Measured switching voltages together with the 1 dB loss curves versus the length of the phase section for the 0.85% tensile- strained sample at 1530 nm. The gray area indicates the allowable voltage—length combinations for less than 1 dB loss. A maximum of 1 dB unbalance requires a phase section longer than 1.7 mm.
Fig. 1. A, The polarized PL spectra taken from a ZnSe/BeTe double-barrier structure at different bias voltages for the analyser orientation along the x’ and y’ axes (7 = 1.6 K). B, The band diagram of the biased sample. C, Effect of an electric field on the polarization of the PL band arising due to optical transitions from the ZnSe emitter to the adjacent BeTe layer.
Fig. 1. Dispersion relations for nine binary semiconductor compounds computed with the parameters listed in Table 1
Fig. 1. Block diagram for CR measurement. A pulsed high-magnetic field up to 150 T is produced by using a single-turn coil technique. The magnetic field is applied parallel to the growth direction of SLs.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 2. Experimental results of CR for (InGaAs),/(GaAs), SLs with n = 6-18 in the transmission of 10.6 jm radiation at room temperature. The resonance at around 75 T gives the cyclotron mass of 0.074n9.
Fig. 3. Experimental results of CR for (InGaAs),/(AlAs), SLs with n = 6-12 in the transmission of 10.6 um radiation at room temperature. The cyclotron masses of the SLs with n = 6, 8, 12 were 0.073mg, 0.078mpo, 0.080mg, respectively.
Fig. 4. Estimated cyclotron masses in (InGaAs),,/(GaAs),, SLs (e) and (InGaAs)n/(AlAs)y SLs (0). A pulsed high-magnetic field up to 150 T is produced by using a single-turn coil technique. The magnetic field is applied parallel to the growth direction of SLs.
Fig. 1. dc current-voltage characteristic for the double-barrier diode. interrogated about its new state? Or how long does it take the RTD to reach equilibrium. We address this problem by recognizing that an important RTD application is as an element in a circuit sustaining relaxation oscillations. In this simple context we may expect that the device to function as a clock at frequencies in excess of 100 GHz. Now negative differential conductance devices when part of an external circuit or trans- mission line, will under suitable conditions respond to pulse-like changes in applied bias with intra-pulse repetitive current-time and voltage—time profiles. This means that the only meaningful study of the response time of the device requires that we incorporate external circuit elements. But we should be able to address some minimal issues such as switching times without the elaborate use of the transmission line. What we have done is to pulse the RTD starting from an initial steady state. In this calculation we include displacement as well as particle current contributions at the contact regions. (In the vicinity of the contacts the density is very nearly equal to the background density and so the total current at the boundaries is well represented by the sum of displacement and particle currents.) One calculation is illustrated in Fig. 2. For this case starting from a steady state in which the applied bias was —8.0 kgT, we dropped the potential energy at a controlled rate to —12.0 kgT, let the device sit at this value for approximately 700 fs, and then returned to the steady-state bias of —8.0 kgT.
Fig. 2. Current density in response to a trapezoidal change in applied bias.
Fig. 3. Spatial distribution of potential energy at three different points in time.
of operation ranges between 100 MHz and 15 GHz. By increasing the permittivity of the dielectric bridge, it is expected that the microstrip transition will provide a better match since the effective dielectric constant (€refp) Of the microstrip line on a GaAs substrate is between 7.54 and 9.81. Thus, for a dielectric bridge with dielectric constant close to €;e¢, the microstrip transition should result in substantially less reflections compared with the air bridge. The dependence of || on the dielectric constant of the bridge is illustrated for d = 3.17a in Fig. 2. As shown, a dielectric bridge with €, = 9.8 provides the best match of all four cases for a normalized frequency of ky -a < 0.2. At higher frequencies, the dielectric bridge, which acts like a resonator, causes the magnitude of S$); to rapidly increase.
Fig. 1. Low-pass filter on a Duroid substrate of €, = 2.2.
Fig. 2. Microstrip transition through a dielectric bridge (d = 3.17a).
obtained using the FDFD method [2]. An increase in the length of the bond wire results in a larger overall S\1. At higher frequencies, the structure resonates thereby forcing $1; to zero. However, compared with the microstrip interconnection through an air bridge, which is shown in Fig. 2, the bond wire creates higher reflections. For example, at a frequency of 4 GHz, a bond wire with length 3.17 mm and height 0.2 mm causes more than 50% reflections. On the contrary, the microstrip interconnection through an air bridge, at the same frequency, causes only 25% reflections. The electrical performance of an MMIC is drastically altered when mounted into a package such as the eight-lead small outline integrated circuit (SOIC-8) surface-mount plastic package shown in Fig. 4. Plastic packages have been used for years up to a frequency of about 2.5 GHz. It becomes extremely difficult to utilize these packages for higher frequencies mainly because of poor grounding of the paddle and package resonances. First, the MMIC shown in Fig. 5 is analysed in the absence of the package. This circuit represents a basic through-connection with a stub. When placed into the package, the circuit itself is elevated 0.1 mm above the ground and embedded into a dielectric medium with dielectric constant ¢, = 4. The same MMIC structure, mounted into the SOIC-8 surface-mount package, was analysed by Jackson [3] using the method
Fig. 5. Geometry of the unpackaged MMIC and corresponding S-parameters.
Fig. 6. Top view of the SOIC-8 plastic package and corresponding S-parameters. of moments (MoM). The S-parameters of the through-connection were calculated using the FEM. The mag- nitude of 5S); and S2; is shown vs. frequency in Fig. 5. It is evident that the circuit resonates at 10 GHz which corresponds to the frequency where the stub becomes quarter of a wavelength long.
Fig. 1. A, Schematic measurement set-up of a quantum dot in SWNT. A constant bias voltage Vgq is applied to the SWNT. The tunnel barrier may exist at the junction of the electrode and SWNT. There is one side gate pad near the SWNT electrostatically coupled to the dot with capacitance Cg. The other side gate is used for the microwave irradiation. B, Temperature dependence of the Coulomb peak current. Inset: Coulomb blockade oscillations of SWNT at increasing temperatures.
Fig. 2. A, /—Vgq characteristics at 4.2 K for gate voltage Vg ranging from —1 to —6 V with an increment of 20 mV. The curves are offset for clarity. B, Gray-scale plot of the differential conductance. the energy level spacing AE = 2.3 meV, which happens to be the similar value to Ec, from the measurements . of Coulomb blockade oscillation for large source—drain bias voltages. The charging energy corresponds to a temperature of about 100 K. By narrowing the distance between the two contacts, we may be able to achieve the Coulomb blockade effect at room temperature in the future. Fae MSE LEAN Te ER AATISAR AMA NRTA SE LT ENe Re AT SEATHIGGEE IAT AEP OaNR ORME ESP A SAMNT GN SERELE he Tae” SORRER NSS SAMI se sie nconewe octenabet dae em In Fig. 3, the effect of the microwave irradiation on J—Vsqg characteristics is shown. The data were taken at the lowest temperature with the microwave power changing from —40 dBm to —12 dBm, while the lowest one corresponds to the curve without irradiation. We should note that the applied microwave power was kept small such that the temperature would not change during the measurement. Without microwave irradiation, the curve shows the Coulomb gap and structures due to the excited state of the OD quantum state. As the microwave power is increased, the curve becomes smooth with less structure. The differential conductance, which is calculated from the J—~Vsq data and shown in the inset of the figure, indicates that the curve become less structured as the microwave power is increased. We have made measurements at different frequencies and at 4.2 K, and observed the similar result. These experimental observations suggest the classical coupling mechanism of high-frequency radiation to the dot. The high-frequency field couples to the source—drain volt- age as an ac source in addition to the dc bias voltage. The measured dc current under microwave irradiation is the time-averaged current over the modulating voltage around the fixed dc bias voltage. This may explain the observed J—Vgq characteristics under microwave irradiation. At the moment, we do not fully understand the reason of the classical coupling even through hf for 20 GHz (~1 K) is larger than kT (~0.25 K) [8-10]. Since special care was not paid to the connection between the coaxial line and the sample gate, the electro- magnetic field around the dot could be very much complicated. The microwave signal may couple to various electrodes with macroscopic dimensions, resulting in the effective modulation of Vgq.
Fig. 1. A schematic diagram of the nanocontact structure utilizing a 4 nm diameter Au cluster, a self-assembled monolayer of xyly dithiol and a GaAs heterostructure with a chemically stable surface layer. Conjugated organic molecules that are difunctional such as aryl dithiols can provide mechanical link- ing/tethering between a cluster and another surface (a cluster or a semiconductor/metal surface) as well as 1 path for electronic conduction between the respective conductors. The specific molecule used for linking the metal nanoclusters to the semiconductor surface in this study is xyly! dithiol (HS-CH2—C~gH4-CH2-SH) which will be referred to as XYL for brevity. This molecule has a length of approximately 1 nm and has thiol (-SH) end groups on each end. These thiol groups can chemically bond to the GaAs surface and to the gold nanoclusters. A self-assembled monolayer (SAM) of XYL is grown on the GaAs surface; given the size of the molecule and the expected packing density, it is believed that a number of XYL molecules (approx- imately 30) are packed within the area of a facet on a 4 nm diameter Au cluster. The interface between a nanocluster and the GaAs surface therefore consists of a small bundle of XYL molecules. XYL is one of aclass of conjugated organic molecules that have been studied as molecular conductors [7— 9]. Such experimental studies typically involve the formation of a self-assembled monolayer (SAM) of the desired molecule on a relatively flat Au surface, with a top contact formed either by metal evaporation, deposition of a metal nanocluster, or by a scanning probe tip (e.g. a scanning tunneling microscope (STM) ip). Theoretical descriptions of the current-voltage relationships have been developed based on the scattering heory of transport. With proper treatment of the Fermi level position in the molecule, of the coupling strength o the contacts and of the capacitive division of the applied voltage, the low-field resistances and current— voltage characteristics for the various experimental reports can be adequately described by this modeling approach [7, 9]. If strong bonding (i.e. strong electronic coupling) to the metallic contacts is realized, vertical rransport through a SAM of a short molecule such as XYL should have a specific resistance on the order of x 1078 Q cm?. el
with the corresponding curves for the measurement over the XYL coated surface (without cluster). The curves shown in Fig. 2 are taken at relatively low set-point currents, corresponding to relatively large tip-to- sample distances. In order to determine the resistance of the nanocontact, i.e. the resistance between the Au nanocluster and the doped layers in the semiconductor structure, it is necessary to reduce the tip-to-cluster distance, and thereby the tip-to-cluster resistance. This has been accomplished by monitoring the current (J) at constant voltage as the tip height (z) is decreased with respect to the height at the low-current set-point. For a structure in which the LTG:GaAs layer is undoped (n-type), the measured / (z) relationship saturates as the tip is brought closer to the cluster. In the saturation regime, the overall resistance should be dominated by the cluster-to-substrate resistance, so the desired nanocontact resistance can be determined from the ratio of the applied voltage to the the saturation current [15]. For this case, the specific contact resistance is approximately 1 x 107° Q cm? and the maximum current density is approximately 1 x 10° A cm~* [15]. For a structure in which the LTG:GaAs layer is heavily doped with Be, as is the case in Fig. 2, values of p, of approximately 1 x 10-7 Q cm? and the maximum current density of approximately 1 x 10’ A cm~? are obtained. Both of these values are comparable to the values achieved in high-quality large-area ohmic contacts to n-type GaAs [16]. In this case, the measurement system limits the minimum , which can be resolved, so the contact resistance may be somewhat lower than this value. Thus, the measured specific contact resistances for the best nanocontact structures are somewhat better than those achieved in the large-area contact studies, indicating that high-performance nanocontacts can be formed to GaAs device layers using this nonalloyed ohmic contact approach.
Fig. 3. A 50 x 50 nm UHV STM topographic image of close-packed 2D array of Au nanoclusters tethered to the XYL-coated semicon- ductor heterostructure with Be-doped LTG:GaAs surface layer, acquired with Vset = —1.2 V and Jset = 0.1 nA.
Fig. 4. Calculated conduction band profile for ohmic contact structure (metal/GaAs) with a 3 nm thick LTG:GaAs layer on the surface. The curve is for a structure with a barrier height of 0.5 eV, a doping density in the nt-GaAs layer of 1 x 1029 cm73 and a temperature of 300 K. Also shown is the parabolic conduction band profile for an equivalent uniformly doped Schottky barrier, assuming complete ionization. versus temperature. Based on comparisons between the experimental results and the predictions, it appears that the surface barrier heights are well below mid-gap values and that activated donor densities above the bulk amphoteric limit have been achieved in the space charge region [17]. It is typically not possible to achieve either of these effects in ex situ contacts to n-type GaAs, due to the surface Fermi level pinning associated with rapid surface oxidation and the bulk amphoteric doping limit in stoichiometric layers. The achievement of both effects in this structure is attributed to the passivating effects of the thin LTG:GaAs layer and to the associated Fermi level control. The ability to achieve an activated donor density within the surface space-charge region which is higher than the bulk amphoteric limit has been explained in terms of the control of Fermi level during growth and the passivation effects of the LTG:GaAs layer [10]. It should be noted that the semiconductor heterostructure is typically exposed to air for prolonged periods before contact processing, so a portion of the LTG:GaAs layer does oxidize during this storage period. Since this oxidation appears to cause mid-gap surface Fermi level pinning even in LTG:GaAs following prolonged air exposure [18], the surface oxide must be stripped shortly before contact metallization. It is believed that the oxide strip restores the surface Fermi level to an unpinned state, with a re-oxidation time constant of hours.
Fig. 1. A, Micrograph of a spin-valve device consisting a single multi-walled carbon nanotube (MWNT) electrically contacted by ferromagnetic Co. The Co contacts lie on top of the MWNT, and the conducting channel is approximately 250 nm in length. B, Two- terminal differential resistance as a function of magnetic field. The magnetic field is directed parallel to the substrate, and the temperature is 4.2 K. The solid (dashed) trace corresponds to the positive (negative) sweep direction. The magnetization direction of the left and right contacts is represented by the direction of the arrows in the figure. The percentage difference AR/Ro between the tunnel resistance in the parallel and the antiparallel states is approximately 6%.
Fig. 2. A, Temperature dependence of the two-terminal differential resistance as a function of magnetic field. B, At low temperatures the positive spin-valve signal comes out. C, The signal almost disappears at 20 K and D, flips to negative at higher temperature. The spin-valve signal eventually disappears at 175 K.
Fig. 3. Micrograph of a single bundle of single-walled carbon nanotubes (SWNTs) electrically contacted by ferromagnetic Co. The Co contacts lie on top of the SWNT, and the conducting channel is approximately 250 nm in length. A side-gate is located at 5 zm apart from the nanotubes. devices, the contact magnetizations align parallel with the magnetic field at B = 100 mT and —100 mT (Fig. 1B). As we sweep B through 0 T, the magnetization polarity switches. The observed peak suggests hat the contact magnetizations switch separately and become misaligned as the field is swept. For a MTJ. misalignment occurs because different ferromagnetic contact materials are used, with different coercivities— the magnetizations are misaligned when B lies between the coercive fields of the two contacts. This does not explain the misalignment in the nanotube device. The misalignment may be caused by magnetization fluctuations that occur locally, on the scale of the nanotube diameter (30 nm). The average Co domain size
Fig. 4. Two-terminal differential resistance normalized by the zero-field resistance as a function of magnetic field at various tempera- tures. When the magnetic field is applied parallel to the contact plane, the magnetoresistance has a peak associated with the spin-valve ef- fect between the two ferromagnetic contacts. The resistances are normalized by each zero-field resistance; 2610 kQ for 10 K, 290 kQ for 15K, 175 k& for 20 K, and 130 kQ for 30 K. Solid lines and dotted lines are taken in different field-scan directions. The gate voltage is 0.
domain with misaligned magnetization under the magnetic field survives at higher temperature than the aligned magnetization. 3.2. Single-walled carbon nanotube For the SWNTs, the transport is more complicated. In the SWNT two-terminal device with a metal contact, single-electron tunneling was observed [8, 9].
Irradiation of InP-asbestos with the pump beam in resonance with the exciton band results in a high density of electron-hole pairs in QWRs. Some of them tunnel from QWRs to template defects and saturates defects sites at the interface. This effect is equivalent to transferring a negative charge on these defects. The remaining electrons relax radiatively within a few nanoseconds in a QWR after finishing the pump pulse [7]. In contrast, all excitations in the template are frozen by the potential barrier. This assumption correlates with the observation of long-living changes of PL spectra of the pumped sample, moreover the pump memory is erasable by exposing the sample to light of frequency below the absorption edge of InP
Fig. 1. PL spectra of (1) bare and (2) InP infilled asbestos under 2.54 eV probe excitation. The 1.88 eV PL band of bare asbestos (3) afte subtracting the Gaussian approximation to the peak centered at 2.28 eV from curve (1). Fig. 2. PL spectra of InP—asbestos excited by the 2.54 eV probe (1), by 1.935 eV pump and 2.54 eV probe (2) and by the probe beam after 40 min since pumping (3). The arrow marks the pump excitation energy.
Fig. 3. A, PL spectra in the probe regime (curve ) and in the pump-probe regime at pump frequencies of (1) 1.906, (2) 1.925, (3) 1.937 and (4) 1.953 eV for the same intensity of pumping. B, Differential PL spectra obtained by subtracting spectrum (i) from pump-probe spectra of corresponding number in the upper panel.
below the pumping frequency. This effect is visualized as a dip in differential spectra (Fig. 3B). In agreement with this mechanism, the higher the pumping frequency, the larger the area of this dip (Fig. 4D). a , " ee OP NP The radial electrical field, which is induced by charges trapped at the interface of QWRs, is proportional to the number of defects and their charge state. Since the number of charged defects is proportional to the area of the PL enhancement peak and assuming that the captured charge density is higher than the density of defects with electron deficit, we may deduce that the magnitude of the electrical field in the pumped volume of the sample exceeds that of the unpumped volume. Due to this field the exciton binding energy in QWRs decreases (Stark effect) and its transition frequency increases, i.e. PL maximum appears ‘blue’ shifted with respect to the pump frequency (Fig. 4B). Consistently, this shift changes in the same manner as the enhancement area changes (Fig. 4D). To summarize, two components of the InP—asbestos contribute to the emission, moreover, the QWR- template interface governs their balance in the total spectrum. The strong energy-selective pumping at a frequency resonant with the exciton PL band was used to separate the contributions to the total PL signal and to reveal the actual width of the exciton emission peak. This separation appears possible due to the difference in the timescale of the relaxation processes in QWRs and the template. The main lesson from this study is that the complication of the energy relaxation in the nanocomposite is the cost of the increase of the binding energy of excitons in structurally confined nanoparticles.
dimers as a result of the 2 x 1 reconstruction; the unreconstructed surface resembling the (100) surface of diamond. Note that the buckled dimers are all tilted in the same direction (symmetric dimer configuration). The dimer bond length is 1.59 A. Molecular dynamics relaxations starting with an untilted configuration resulted in the formation of asymmetric tilted dimers. The symmetric tilted dimer configuration shown in Fig. 2A is found to be isoenergetic with the asymmetric case. As seen in the figure, the surface dimers are all aligned along the circumference.
Fig. 3. A, ‘Superatom’ cluster unit for QOD structures belonging to (class 2) B, and a section of QCD (class 2) wire obtained by stacking the superatom on top of each other and performing GTBMD relaxation.
Fig. 1. SIMS results for a 600 nm SiO on Si structure following three different deuterium anneals.
Fig. 2. A, Comparison of three different reliability parameters to a H-passivated device following different deuterium annealing condi- tions. B, Comparison of transistor lifetime to a H-passivated device following different deuterium annealing conditions.
Fig. 4. A, A V-shaped pattern of dangling bonds is generated with FCL. The image size is 170 x 170 A2. The insets show individual molecules bound to the surface following exposure to CuPc. The white arrow indicates that some of the sites remain unreacted following this sub-monolayer dose. B, A filled states image of the surface following CuPc exposure illustrates STM tip induced motion of two of the binding sites. The inset d7/dV map was taken at an empty states energy of 2 eV and shows a ring of reduced LDOS surrounding the CuPc molecules.
Fig. 3. FCL is used to generate a 3 x 3 array of dangling bonds on the Si(100)-2X1:H surface. The desorption event is detected as a 15A discontinuity in the tip position (z) after which the patterning conditions of 3 V, 2 nA are terminated. and 0.1 nA tunneling current. It should be noted that the previous position of the dangling bond now appears to be hydrogen passivated. Consequently, under these imaging conditions, the STM can occasionally induce the exchange of H atoms and CuPc molecules along dimer rows. A similar behavior has been observed for the black circled dangling bond site of Fig. 4. In this case, however, the tunneling conductance map after manipulation does not possess a ring of reduced LDOS. Apparently, this site no longer possesses a CuPc molecule. This observation implies that the STM can also induce desorption of CuPc from the surface. By scanning under less perturbative conditions (e.g. reduced tunneling current), unintentional manipulation of CuPc by the STM tip can be avoided.
Fig. 5. A-C, A series of STM images taken after a FCL pattern had been exposed to CuPc. Molecule #1 appears to be stationary, whereas molecule #2 is spinning on the surface. D,E, Two STM images of an ammonia-reacted CuPc molecule after isolation on the $i(100)-2X1:H surface. F, A scaled drawing of CuPc has been overlaid on the image from part E, of this figure. This depiction illustrates the 32 A circle that is swept out by the molecule when it rotates via its outer benzene ring.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000
Fig. 2. A, Coherent optical phonon oscillations in the time domain for bulk GaAs and GaAs/Alp 36Gag.64As MQW with Ly = 15 nm and Ly = 5 nm. B, The Fourier transform in the frequency domain. At high densities, the photoexcited electrons can not screen the LO mode in the MQW since the plasma dispersion varies from the bulk dispersion.
Fig. 3. Transient transmission changes versus probe delay for a 50/43 A InGaN/GaN MQW and a laser wavelength of 365 nm. Hug coherent acoustic phonon oscillations are now observed.
Fig. 1. Coulomb blockade oscillations in a quasi-metallic nanowire showing almost perfect periodicity.
Fig. 2. A, Dependence of the conductance g of an inversion quantum dot on gate voltage Vrg. Coulomb blockade is observed near threshold voltage. B, Temperature dependence of the [5 p—Vsp trace of the dot at a top gate voltage of Vrg = 4.5 V. At 300 K clear single-electron effects remain visible.
Fig. 3. Resonance curves of the reflected rf power of the suspended wire shown in the inset. The resonator is driven into the nonlineat regime by the Lorentz force in a B-field of 12 T applied perpendicularly to the rf current. Different curves are measured at different values of the voltage on one of the sidegates. Inset: SEM micrograph of the structure.
Fig. 1. Schematic diagrams of A, C-SET and B, R-SET with their Coulomb diamonds.
Fig. 2. SEM micrograph of the fabricated device. The measurement set-up is also shown.
Fig. 3. Observed Coulomb diamonds. A, |/| = 0.03, 0.06,...,0.18 nA. Vj = —1.194 V, Vo = —1.324 V, V3 = —0.444 V, V4 = —0.444 V, Vej = —0.52 V.B, |7| = 0.1,0.2,...,0.6 nA. Vy = —1.228 V, Vo = —1.333 V, V3 = —0.415 V, V4 = —0.415 V, Voi = —0.52 V.
Fig. 4. Calculated Coulomb diamonds. A, |J/(e/RxCy)| = 5, 10,...,35. Re/R1 = Rg/Rz = 100, Cg/Cy — Cg/Cz = 1, U/(KT) = 100, Qo/e = —0.2. B, |//(e/ReCx)| = 0.1,0.2,...,1.0. Re/Ry = Re/R2 = 1, Cg/C) = Cg/Cy = 10, U/(KT) = 100, Qo/e = —0.2.
Denoted by W,; is the connection weight to neuron i from neuron j, and 6; is the bias-connection weight to neuron i from a bias that fixed at the value of 1, and u; is the output of neuron i. A set of neuron outputs (uy, U2, ...) is called the state of the network. In this network, each neuron / takes a weighted sum s; of its inputs (s; = )> j Wijuj +49) and generates the corresponding output u; according to a given staircase transfer function. All neurons operate in parallel to update their outputs continuously, and the network converges to an optimal state through the updating process.
To solve this problem, we prepare a multiple-valued Hopfield network such that the output u; of each neuron represents each problem variable x;; we prepare neurons with the staircase transfer function illustrated in Fig. 2 and represent problem variables x; by x; = u;/a. The connection weights required for mapping the problem are given in Fig. 2. In problem solving, we set the network in an initial state (any state will do), then allow it to change its state without restraint. After some transition time the network converges to a final state. If convergence has been successful, the solution to the problem is obtained from the final state of the network (we will not discuss the local-minimum effect here). 3. Constructing a multiple-valued neuron using single-electron circuits The single-electron circuit is an electronic circuit consisting of tunnel junctions and capacitors that is de- signed for manipulating electronic functions by controlling the transport of individual electrons. The internal state of the circuit is determined by the configuration of its electrons (i.e. the pattern in which the excess elec- trons are distributed among the nodes of the circuit). The circuit changes its electron configuration through electron tunnelings in response to the input and, thereby, changes its output voltage as a function of inputs. etree, a a SO ~ Our purpose is to construct a single-electron neuron circuit that changes the charge on its output node (therefore its output voltage) according to a staircase function of the input voltage. For this purpose, we take Tucker’s single-electron inverter and modify its circuit parameters to create a staircase transfer function (for the details of Tucker’s original circuit, see [1]). The circuit we use for the neuron devices is illustrated in Fig. 3 together with a sample set of device parameters. The corresponding transfer characteristic are illustrated in Fig. 4. The number of steps in the transfer characteristic can be controlled by designing the circuit parameters.
Fig. 2. Principle of bit-comparison using Coulomb repulsion effect (A), and two word-comparator circuits (B, C).
Fig. 1. Associative memory architecture.
Superlattices and Microstructures, Vol. 27, No. 5/6, 2000 Fig. 3. Three-dimensional structure image of a word-comparator (circuit-A).
Fig. 4. Simulation results for circuit-A: A, operation temperature range with one BC; B, output voltage changes at room temperature; and C, setting margin for Co. “i
Fig. 2. J-V for SET arrays with N = 20 (cross), 60 (hollow triangle) and 120 (filled triangle), capacitances scaled as described in th text. Dots indicate drift-diffusion calculations. Equations (2), (4) and (5) are solved self-consistently and represent the motion of a collection of over- damped, interacting particles undergoing gradient flow. In contrast to the normal case, however, E is the total, interacting free energy of the system, rather than an externally imposed potential. We have only used the assumption that the particle motion proceeds via tunneling in eqn (4) where we find that the velocity is proportional to the energy gradient. Thus, we may re-interpret the proportionality constant as a reciprocal mass-viscosity, 1/my or, via Einstein’s relation, we may write
Fig. 1. Competition between Coulomb blockade and Cooper pair tunneling.
Fig. 2. Voltage-biased S-SET. RY, C; are tunnel resistance and capacitance of the junction i and Q; is the charge induced on the electrode i with chemical potential n;.Cy = pe C; and C = C}C2/Cy. Zj)(w) = iwL; etc., for simplicity.
level is strongly localized in one of the InGaAs wells. The ground heavy-hole state localizes in the well that shows a large red shift, the first excited state localizes in the middle well and the second excited state localizes in the well which shows a blue shift. As a consequence, the net QCSE red shift in a CQW is two times larger than in a 110 A Ing.6Gao,4Aso.85Po,15 quantum well.
Table 1: Bandstructure model parameters. All energies are in units of eV and the lattice constant is in units of nm. that the sp3s* nearest-neighbor model pathologically predicts an infinite transverse mass at the X-point [2, 3]. With the limitations of the sp3s* model in mind it must be emphasized that early parametrizations [1] pro- vided more global band structure fits for bands which can be probed by optical measurements. The compli- cation in the fitting process of the 15 orbital interaction energies to measurable quantities has led to the use of the seminal Vogl [1] parameters in areas in which they were not intended. For example, quantitative electron transport simulations in high-performance resonant tunneling diodes [4] require the proper representation of relative band energies as well as band curvature of the conduction and valence bands, even for a purely electronic device (no hole transport).
masses and band edges of the lowest conduction and three highest valence bands are considered. Including the '7,, L7_ and X7_ with higher than nominal weights keeps the upper conduction bands well above the lowest conduction band. The agreement with the L¢, value must be driven towards cautiously as a minima on the A line starts to develop instead of the minimum at the L-point.
Table 1: Relative energies of the carbon nanowire clusters obtained using the present scheme. All energies are relative to the (10,10) capsule shown Fig. 1. The values of the energy difference between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are also given.
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The Kondo Effect and The Kondo Problem
by Dr. J. M. Ashfaque (MInstP)
It is known that for certain metals with magnetic impurities, the resistivity decreases as temperature decreases but then reaches a minimum and after that it increases as − ln T as the temperature decreases further. Moreover, the... more
FIG. 1. Impurity Electron at €;, conduction electron at ez and excited state at ¢; + U. (a) Process where first a conduction electron jumps to an excited state. (b) Process where first the impurity electron jumps to a conduction state. We apply this to the case where the impurity energy e€,; is situated in the middle of the conduction band, the conduction states ez and ez, are at the upper side of it and the excited impurity state is above the conduction band, at e; + U as can been seen in the diagram below. Then consid er the two possible processes. First, the conduction electron jumps to the opposit e spin excited impurity state then the impurity electron jumps to the conduction electron state as can be seen in Fig. 1 (a). te and then the conduction electron jumps to the excited impurity state as in Fig. 1 electron sta the first pro FEinitial = The other possibility is that first the impurity electron jumps to the opposite spin cond uction b). In cess, Hintermediate = 2€; + U and in the second Ejntermediate = €g + €g- In both the cases + ez. Also, in both cases, there is a minus sign in the amplitude due to the exchange final state o processes, w in the f the two electrons (fermions) between the conduction and the impurity. Adding up t e obtain he two
where D is the maximum energy in the conduction band for the electrons. We can do the k and ez integrals obtaining with indices 2/1 corresponding to the + signs, respectively. We now convert the sums J, and I, into integrals using the total density of states at momentum k, p = mk/(77h?) and ez = k?/(2m) to obtain All in all, at second-order in perturbation we have
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Physical characterization of thin-film solar cells
by Wyatt Metzger

2004, Progress in Photovoltaics: Research and Applications

The principal techniques used in the physical characterization of thin-film solar cells and materials are reviewed, these being scanning probe microscopy (SPM), X-ray diffraction (XRD), spectroscopic ellipsometry, transmission electron... more
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Permanent magnet applications
by Jmd Coey

2002, Journal of magnetism and magnetic materials

Rare-earth permanent magnets are ideally suited to generate magnetic fields comparable to their spontaneous polarization J S : Near-square hysteresis loops and large values of the coercivity and anisotropy fields greatly simplify magnet... more
Fig. 1. Summary of permanent magnet applications.
Intrinsic magnetic properties of phases used in permanent magnet manufacture Fig. 2. Comparison of the magnetic field pattern produced: (a) by a point dipole of moment m, and (b) a line dipole with moment / per unit length. Table 4
Fig. 3. Cross-section of some permanent magnet structures which generate a uniform magnetic field in the direction shown by the hollow arrow. Magnets are unshaded; the shaded material is soft-iron. J.M.D. Coey | Journal of Magnetism and Magnetic Materials 248 (2002) 441-456
Fig. 4. Cross-section of some permanent magnet structures which generate non-uniform magnetic fields (a), (b) quadrupole fields, (c) an external quadrupole field, and (d) a field gradient. J.M.D. Coey | Journal of Magnetism and Magnetic Materials 248 (2002) 441-456
Fig. 5. Periodic flux sources: (a) a magnet for a microwave travelling-wave tube and (b) a wiggler magnet used to generate intense electromagnetic radiation from an electron beam. Simple force applications in catches and closures consume large amounts of sintered ferrite. Bonded
Fig. 6. Two design for switchable permanent magnets.
Fig. 7. Permanent magnet variable flux sources: (a) a double Halbach cylinder, (b) a four-rod magnetic mangle, and (c) an external dipole ring with a movable iron sheath.
Fig. 8. Some magnetic bearings and couplings: (a) is a linear bearing, (b) and (c) are rotary bearings, (d) is a face-type coupling and (e) is a magnetic gear. J.M.D. Coey | Journal of Magnetism and Magnetic Materials 248 (2002) 441-456
Fig. 9. Images of a permanent magnet in: (a) a soft ferromagnet and (b) a superconductor or strong diamagnet. belt carries the rubbish over a static or rotating drum with embedded ferrite or rare-earth magnets. The relative velocity of the magnets and the refuse may be 50ms~'. Eddy currents induced in the metal create a repulsive field, and the metal is thrown off the end of the belt in a different direction to the nonmetallic waste. In electromag- netic separation, deflection depends on the ratio of conductivity to density, so it is possible to separate metals such as aluminium, brass and copper. difficulty in establishing the flux in the super- conductor, and the need for cooling.
Fig. 10. Electromagnetic separation with permanent magnets.
Fig. 11. A flat voice-coil actuator for a personal-computer disk drive.
Fig. 12. DC motor designs: (a) brush motor with magnets on the stator and (b) brushless motor with magnets on the rotor J.M.D. Coey | Journal of Magnetism and Magnetic Materials 248 (2002) 441-456
Summary of permanent magnet applications Table 1 L aligned perpendicular to the field, as in the armature of a motor or actuator, they constitute a current 7, and the Lorentz force leads to the familiar expression F = BIL. Conversely, moving a conductor through the field produces an induced emf given by Faraday’s law e = —d@/dt where ® is the flux threading the circuit of which the conductor forms a part.
Characteristics of typical commercial-oriented magnets *Intergrown with 1:5 phase.
Temperature coefficients and maximum operating temperatures for permanent magnets *Intergrown with 1:5 phase.
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Non-thermal plasma treatment of textiles
by Nathalie De Geyter and 
1 more
P. Kiekens

2008, Surface and Coatings Technology

This article attempts to give an overview of the literature on the treatment of textiles with non-thermal plasmas. Because of the enormous amount of potential uses of non-thermal plasmas for the modification of textile products,... more
Fig. 2. Water contact angle of different time plasma-treated PP (left) and PET (right) fibres versus storage time at ambient temperature [285]
Fig. 4. Water-repellent properties of cotton fabrics treated with DEAEPN (a) before and (b) after grafting and polymerisation of AC8, washing, and drying at 373 K [287].
Fig. 5. Effect of microwave plasma cleaning with different gas mixtures and varying pressure [288]. Cai et al. [176] applied air/He and air/O,/He atmospheric plasma treatments to desize PVA on cotton. The air/O,/He reatment showed to have a greater effect on PVA than the air/He plasma. Both plasma treatments did not only serve to remove some PVA size, but also to significantly facilitate PVA removal by subsequent washing. The authors attributed this effect to the enhanced swelling, dissolving and dispersing of PVA. The ensile strengths of the fabrics and yarns were not statistically significantly affected by the plasma treatment. The same authors also applied both treatments for desizing PVA on rayon (viscose) fabrics [177]. Both treatments were able to remove some of the PVA on the rayon and increase PVA solubility in cold water, resulting in a higher weight loss in cold washing. The effect of he atmospheric pressure plasmas became greater as the treat- A comparative study between plasma and wet chemical cleaning of synthetic fibres was done by Keller et al. [182]. In this work, different cleaning methods were compared in order to remove sizes on PET multifilament fibres, namely chemical
Fig. 6. Characteristic survival curve for micro-organisms on a PP sample containing an initial loading of 6x 10° Z. coli K12 cells treated by an OAUGDP [289].
Fig. 7. 3D views of AFM images of PET textile surface. (a) Untreated surface; (b) 60 s treated surface; (c) 120 s treated surface [290]. Plasma treatments can improve properties such as (tear) strength, elongation, stiffness, etc. A number of studies were published by Thorsen from the second half of the 1960s onwards on improved frictional properties of fibres by AC corona treatment at atmospheric pressure [205—207]. The tensile strength of wool, mohair and cotton yarns increases with 12—26%, 31% and 28% respectively, even after treatment as short as | s. This frictionising can further lead to improved mohair carding and to an increase in wool fibre spinning rate into yarns and improved cotton spinnability. McCord et al. demonstrated the effect of gas composition of the plasma on tensile strength of nylon [208]. They had a slight decrease in nylon fabric tensile strength after treatment in He for 3 min, while there was no significant change in tensile strength of the nylon fabric treated with He—O, after exposure times of up to 8 min. Belin et al. [209] showed that cotton sliver tenacity was improved for a single corona passage and even more for three consecutive passes. They also observed an improved wettability and dye adsorption [210]. In the former case, increased felting The treatment of PET fabrics in a SiCl, plasma has been done to improve their comfort-related mechanical and surface properties [30]. The primary effect of the plasma treatment was on the surface roughness, in good accordance with atomic force microscopy (AFM) roughness data. A similar AFM study was
Wettability of wool, polyester, and polyamide 6 fabrics treated with corona discharge [37]
Contact angle of silk and cotton fabrics treated by C3F¢ plasma for various treatment times [150] Table 2
Change in whiteness of wool of different fineness treated with a gliding discharge in different environments [199]
Wettability and antistatic ability of the untreated and plasma-treated samples [243]
Values of the DFE for (non) plasma-treated woollen fibres [248] Table 5
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Titanium oxide nanotube arrays prepared by anodic oxidation
by Faton Podrimqaku

2001, Journal of Materials …

Titanium oxide nanotubes were fabricated by anodic oxidation of a pure titanium sheet in an aqueous solution containing 0.5 to 3.5 wt% hydrofluoric acid. These tubes are well aligned and organized into high-density uniform arrays. While... more
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Formation of carbon supported PtRu alloys: an XRD analysis
by francesco cardellini

2001, Journal of Alloys and Compounds

Carbon supported PtRu alloys were prepared by impregnation of Pt and Ru precursors on a porous carbon support, followed by reduction of the metals with Na S O . After reduction, the samples were thermal treated in argon up to 7008C. The... more
Fig. 1. X-ray diffraction pattern of carbon (KJB) supported platinum, thermal treated at 400°C.
Fig. 2. X-ray diffraction patterns of carbon (KJB) supported PtRu with nominal Pt:Ru 1:1, thermal treated at different temperatures.
Fig. 3. PtRu[111]/C[0015] peak height ratio vs. thermal treatment temperature. took place starting from 300°C, and the intensity of PtRu[111] reflexion increased, owing to the increase of the crystallinity, up to around 450°C. Then the PtRu[111] peak
Fig. 4. Dependence of PtRu d-spacing for [220] (a) and [311] {b) reflexions on thermal treatment temperature (d-spacing error+0.001 A). The dependence of d-spacing of PtRu[220] and PtRu[311] reflexions on thermal treatment temperature is shown in Fig. 4a,b. The d-spacing of both reflexions decreased with increasing annealing temperature. This reduction in d-spacing corresponds to a reduction of the attice parameter, resulting from the replacement of the platinum atoms on the lattice points of the f.c.c. crystal structure by the smaller ruthenium atoms. From d-spacing values of [220] and [311] reflexions, we have calculated the lattice parameter of PtRu alloys. Fig. 5 shows the dependence of PtRu lattice parameter on thermal treatment temperature. Lattice constant values were lower than that of pure platinum supported on KJB (upper dashed line), and higher than that of unsupported PtRu alloy with Pt:Ru atomic ratio 1:1(lower dashed line). The lattice parameter decreased with increasing temperature. The lowest value of the lattice parameter was similar to the value of the lattice
Fig. 5. PtRu lattice constant vs. thermal treatment temperature. Lattice parameter error+0.0025 A. (@) PtRu/C (KJB) with Pt:Ru atomic ratio 1:1; (O) PtRu/C (V) with Pt:Ru 1:3; (upper dashed line) pure Pt on KJB carbon thermal treated at 400°C; (lower dashed line) unsupported PtRu with Pt:Ru 1:1 [6].
Ru a. He Fig. 6. X-ray diffraction pattern of carbon (V) supported PtRu with Pt:Ru atomic ratio 1:3, thermally untreated.
Fig. 7. Dependence of Ru alloyed on thermal treatment temperature. References
Fig. 8. Arrhenius plot of Ru alloyed against 1/T. process. Fig. 8 shows the dependence of In Ru,, on the reciprocal of absolute temperature. The linearity of the plot attests the presence of a diffusion process. The value of E, was 34 kJ mol”’. On the basis of the plot shown in Fig. 8 the percent of Ru alloyed by diffusion process in the absence of thermal treatment should be about zero. The value of alloyed Ru of untreated PtRu supported on V with Pt:Ru 1:3, instead, was 4%. In the presence of an excess of Ru or/and of a different carbon support (different metal- support interactions), perhaps Ru atoms substitute Pt atoms into f.c.c. structure during the formation of the crystallites.
Ru atomic fraction in PtRu alloys, calculated from Eq. (1)* * Ru atomic fraction error+0.02. Table 1
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The Charged-Photon Model of the Electron Fits the Schrödinger Equation
by Richard Gauthier
This article shows how the charged photon model of the electron is consistent with the time-dependent and the time-independent forms of the one-dimensional Schrödinger equation, which describes the conservation of total energy of a... more
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An updated overview of diamond-like carbon coating in tribology
by Hasan Mahmud and 
1 more
HM Mobarak
During the last two decades, the industry (including scientists) has focused on diamond-like carbon (DLC) coating because of its wide range of application in various fields. This material has numerous applications in mechanical,... more
FIG. 1. Ternary phase diagram for various DLC films with respect to their sp*, sp* type bonding and hydrogen content in the structure. (© Elsevier. Reproduced with permission of Love et al.'® Permission to reuse must be obtained from the rightsholder.)
FIG. 2. Schematic diagram of different deposition techniques (A) ion beam deposition technique,' (B) magnetron sputtering,” (C) plasma immersion ion implantation and deposition ioint, and (D) plasma activated chemical vapor deposition.”
FIG. 4. Coefficient of friction and wear property variation with respect to temperature of the Tungsten-doped DLC coating. (© Elsevier. Reproduced with permission of Gharam et al.°* Permission to reuse must be obtained from the rightsholder.) hyd DL wil obs C. If ta-C film is annealed in vacuum, then t Phase transformation and oxidation temperature for non rogenated DLC is much higher than that for hydrogenated he structure be stable up to 727°C. If heated in air, film oxidation is erved from 450-500°C.*8 Therefore, the CoF of non hydro- genated DLC will be stable at higher temperature compared to hyd rogenated DLC. Behavior of non hydrogenated car by magnetron sputtering are reported to be therma to 300°C. Beyond 300°C, the hardness value drastically drops because of graphitization of the coating structure. CoF increases at elevated temperature testing. The increased fric- tion coefficient is due to the absence of water in the trib ocontact. 98 amorphous bon a-C is different from ta-C. DLC (a-C) film deposited ly stable up 2.4.3.1. Silicon Containing DLC. Tkeyama et al.”® inves- tigated the property of DLC coating doped with Si. Si doping releases internal stress, which results in decreased hardness. Si Some metals and non metals can be added as a dopant to enhance some coating properties mentioned in earlier section (Section 2.1). Their effects will be discussed briefly in the fol- lowing sections.
FIG. 5. (A) Friction coefficient change with different velocity at a normal load of 20.7N. (B) Friction coefficient change at dif- ferent load with the change of velocity. (© Elsevier. Reproduced with permission of Kim and Kim.'*° Permission to reuse must be obtained from the rightsholder.) where AT is the induced temperature rise, ft is the CoF, P is the applied normal load, v is the sliding speed, K; and K, are the thermal conductivities of the coating and the ball, respectively, a is the contact radius of t! he real contact area, and H is the measured coating hardness. According to Eq. (1), with the increase of sliding speed v and lo temperature increases; therefore, grap Graphitization results in the lowering of load lowers the graphitization temperatu ad P, contact surface hitization enhances. CoF. Increasing the re by increasing the contact stress. Further graphitization can be promoted by fric- tion-induced annealing on the local contact areas and sliding- induced strain energy.'40'*8 Kim et al.'4° showed the change in CoF at different velocities and normal load. They found the results accord- ing to Figure 5. Figure 5A shows the change of CoF at
FIG. 6. Friction coefficient vs. number of passes at dry and humid condition between different pair of surfaces at a load of 9.8 and velocity 1.6 cm/s. (© Cambridge University Press. Reproduced with permission of Jia et al.'*? Permission to reuse must be obtained from the rightsholder.) Ronkainen et al.” showed the effect of counter face at differ- ent sliding velocity and normal load to the CoF. They used steel and aluminum counterpart and found in both cases CoF decreased with the increment of sliding velocity and normal load. In the case of aluminum counter face, the increase of sliding velocity results in less pronounced trend of decreasing CoF for a-C:H coating (Figure 7). Friction property varies with the type of counter face, material hardness of counter face, and roughness of surface.'*°
Classification and corresponding chemical nomenclature of analyzed additives
FIG. 7. The friction coefficient values at the end of the tests for (a) a-C:H coating sliding against steel (AISI 52100), (b) ta-C coating sliding against steel, (c) a-C:H coating sliding against alumina, and (d) ta-C coatings sliding against alumina in pin-on- disc tests with different sliding. (© Elsevier. Reproduced with permission of Ronkainen et al.” Permission to reuse must be obtained from the rightsholder.)
FIG. 8. Wear coefficient vs. temperature for 7 and 10 N applied normal loads. (© Elsevier. Reproduced with permis- sion of Veverkova and Hainsworth.'®! Permission to reuse must be obtained from the rightsholder.)
FIG. 9. Wear volume (a) and wear rate (b) of DLC coating at different load and velocity. (© Elsevier. Reproduced with permis- sion of Kim and Kim.'** Permission to reuse must be obtained from the rightsholder.) Counter face has a direct impact on the wear behavior of the DLC coating. Table 4 shows the effect of counter face on the wear behavior of the DLC coating and mating surfaces at humid and dry conditions. !*? Si3N, ball has a lower wear rate in dry condition compared to steel ball. However, when the condition is humid, the steel ball has lower wear rate com- pared to the Si3;N, ball. Thus, some kinds of tribochemical reaction favored the wear property of the steel ball in humid condition. Veverkova et al.'®! found that during the pin-on- disk test, steel versus W—DLC showed higher wear rate com- pared to W—DLC/DLC coating pair, which might be due to tri- bolayer formation in the counter faces. The formation of Hydrogen stabilizes the random covalent network of DLC coating and prevents this network from graphitization. Lubri- cant works as a coolant; when this substance is added, the con- tact temperature remains within the allowable range. Therefore, graphitization will not take place. As a result, tribo- chemical interactions of DLC and additives become dominant. Some researchers found that a-C DLC provides low CoF than a-C:H DLC in lubricated condition. Higher surface energy leads to better interaction with a-C:H DLC. Surface energy is low for a-C:H because of the difference in their molecular structure. When high temperature is generated during the slid- ing friction in contact, sp? to sp” conversion of the bond takes place. This sp- bond type represents the graphite-like
FIG. 10. (A) Wear loss and (B) coefficient of friction of selected material combinations using mineral oils with additives (A W/ EP and EP) and without additives. (© Elsevier. Modified with permission of Kalin and Vizintin.'*? Permission to reuse must be obtained from the rightsholder.)
FIG. 11. (a) Wear loss and (b) coefficient of friction of selected material combinations with sunflower oil with additives (AW/ EP and EP) and without additives. (© Elsevier. Modified with permission of Kalin and Vizintin.'*? Permission to reuse must be obtained from the rightsholder.) EP additives are additives for lubricants, which have a function in dec reasing the wear of the parts of engine compo- nents exposed to very high pressures. Therefore, the coating to the engine components, which is exposed to high pressure might have the possibility to interact with EP additives. Thus, the study of EP additive to different types of DLC coating interaction has become important. Non doped DLC is compar- atively inert towards the additive coating interaction. How- ever, when t his material is doped with metal, some interactions take place between the DLC and the additive because metal has higher surface energy. Some studies on the tribological characteristics of steel/DLC contacts have been 186, 1 conducted. ~” 89.197 Kalin et al.!7 investigated the interaction of metal-doped (Ti, WC) DLC with EP additive in tribological and static condition. They investigated the wear and friction property of metal doped, non doped, and steel self-mated con- tact in the presence of mineral oil and additive-added mineral oil. In each case, additive-added mineral oil shows lower wear rate; however, no significant change of friction property is observed. The change of wear rate is greater for metal-doped DLC coating. Non doped hydrogenated DLC coating shows low friction in the absence of additive. However, oil additive blend shows higher friction because in the presence of addi- tive, a viscous tribofilm is formed in the non doped hydroge- nated DLC coating surface and this oil additive hinders the motion. Through this reaction, friction increases, but wear property enhances because the tribofilm protects the coating layer.'7!°°:1°8 For uncoated steel surface, maximum wear causes adhesion when tested in oil-lubricated condition. How- ever, when additive is added, adhesion is minimized. Same case is true for metal-doped DLC coating. In every case, tribo- film formation takes place; therefore, different degrees of reac- tivity are observed among different coating surfaces. Kalin 1.!°” showed that Ti-doped DLC coating have high reactiv- ity compared to WC-doped DLC and non doped hydrogenated DLC coating. They observed a difference in phosphorus/sulfur (P/S) ratio after the friction and wear test in the worn surface
FIG. 13 (a) Typical triglyceride composition (vegetable oil) with three different types of fatty acids having different level of saturation (number of double bonds). (b) A schematic of boundary lubrication mechanism on metal surface via adsorp- tion of the polar group from oil or additive. (© Elsevier. Reproduced with permission of Kalin et al.'°° Permission to reuse must be obtained from the rightsholder.) by XPS analysis. P and S come from the additive (EP), the ratio in the additive components is 0.5 (P/S) as shown in Table 4. However, in the worn surface, the ratio is changing because of some reactivity towards the surface. Ti-doped DLC worn surface have 10 times higher P/S ratio compared to the other tested coating surfaces. Oxide formation is actually important. Ti has a higher reactivity with oxygen and forms TiO and TiO. TiO, is the most stable phase of the Ti com- pounds. Friction heating enhances TiO, formation and some
Fig. 12. Schematic presentation of the effect of polar groups and unsaturation of molecules on tribological properties in metal contacts and oxidation stability of selected oils. (© Elsevier. Reproduced with permission of Kalin et al.!°° Permission to reuse must be obtained from the rightsholder.)
FIG. 15. Electrochemical process of the MoS, formation from MoDTC. (© Elsevier. Reproduced with permission of Barros Bouchet et al.'®° Permission to reuse must be obtained from the rightsholder.)
FIG. 14. Molecular structure: a. Moly dimer and b. Moly trimer. (© Elsevier. Reproduced with permission of Kalin et al.°°° Permission to reuse must be obtained from the rightsholder.)
FIG. 16. Schematic view of friction induced hydroxylated-ter- minated carbon surfaces. (© Springer. Reproduced with per- mission of Kano et al.*°’ Permission to reuse must be obtained from the rightsholder.)
Friction coeffecient and wear rate of different types of DLC coating in different environmental condition’? uv refers to coeffecient of friction K refers to wear rate [x10~-°mm3(N m)/] Me refers to metal, such as W,Ti, Mo, Fe, V... X refers to nonmetal, such as Si, O, N, F, B... TABLE 1
Different types of coating applied to engine parts
Different doped DLC coating changes in structure and effect in hardness
Wear rate and friction coefficient at a load of 1 Kg and 1200 m sliding distance. (© Cambridge University Press. Reproduced with permission of Jia et al.'*° Permission to reuse must be obtained from the rightsholder)
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Special Relativity Hypothesis Reason (Matter Creation Theory
by Gerges Tawadrous
Why there's No velocity higher than Light Velocity C =300000 km/sec? Because • The Matter is created from light beams coherence (according to Young Experiment-The Main Hypothesis) • The Time is created as the Matter Changing measurement •... more
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